[orca-list] Pluginsystem for Orca using libpeas

[chrys <chrys linux-a11y org>]

Hello Joanie, Hello list,

i know there are plans to create a plugin system for orca. i created 
SOPS to work around a bit but it does not replace something "real".
Joanie suggested libpeas. I just got some spare time to dive into this. 
I read some documentation about libpeas and it sounds very reasonable to 
me. it provides all the stuff what a plugin system need already.
libpeas plugin engine has the ability to load plugins wirtten python 2, 
python 3, C, and Lua. what sounds very impressive. special C looks like 
an benefit if we need to squeeze out every bit of performance.
So i checked out how libpeas is working and started with an basic plugin 
system for orca what i just want to introduce here.

# Why i did this:
- Orcas code needs IMO to be be cleaned. its a mixture of Object 
Orientation and Procedual programming. Migrating things step by step 
over to an plugin driven architecture would allow us to clean up thins 
step by step and modernize it to an bright future :).
- Users can easy share addons and additional functionality, well thats 
the point of an plugin system :).
- Users can overload orcas "core" plugins if different behave is 
prefered or requred.
- coding is fun

# What i did:
- I create a new Class PluginSystemManager what does all the plugin 
handling and loading / unloading stuff
- there are currently 3 types of plugins handled:
    1. Core: the idea is to port in midterm orcas core functionality to 
this plugin layer. it will provide the basic functionality what is not 
allowed to be unloaded. its living in orcas install path
    2. System: here we can deploy system wide plugins. those can be 
activated and deactivated. its living in orcas install path
    3. User: can be installed per user to be able to customize orca 
individual or without root access. is living in the orca settings of the 
user
- an API class to share orcas API with the plugins. it contains the API 
to fire signals and the signals itself. There are currently just 2 signals:
    1. start-orca: is fired after orca is completly initialized
    2. stop-orca: is fired while stopping orca
- an APIHelper class with some common stuff needed by the plugins more 
often. Lets say a collection of useful functions.
- integrate into build system
- create 2 core plugins  and 3 system plugins just for prototyping and 
try out different things. i reused some code from SOPS. The idea is to 
load all needed plugins on startup. the plugins can register keyboard 
shortcuts or connect to signals while an do_activate and remove them 
while do_deactivate.
    - The core Plugins:
        1. HelloOrca: startup notification of orca, consuming the 
"start-orca" signal (so you will hear "screenreader on" now twice, once 
still hard coded, once by the plugin
        2. ByeOrca: stop notification of orca, consuming the 
"stop-orca" signal (so you will hear "screenreader off" now twice, once 
still hard coded, once by the plugin
    - The system Plugins
        1. helloworld: just prints some debug output and says hello on 
startup
        2. SelfVoice: starts / stops an listening thread when plugin is 
enabled. it waits for incoming text using unix sockets. the text is just 
spoken.
        3. Clipboard: registers an keyboard shortcut Orca + w. it 
announces the content of the current clipboard

# what is currently missing:
- A GUI for Plugin management - a plugin manager (Enable Disable 
Configure). Currently just all available plugins are loaded. i currently 
work on this.
- The setting management is not done yet. (not important as there is no 
plugin  manager to change the settings currently lol)
- integrate more events (this could happen by migrate the current 
functionality step by step)

what do you guys think?
@Joanie, what do you think?
is this worth to be continued?

you can find my work currently on github:
https://github.com/chrys87/orca-plugin

sorry that i just started without ask or something. I don't want to make 
anybody angry. i just tried and played a little. it was something like 
an "selfrunner" + it was really fun to me to do so.
IMO its an chance to modernize the codebase step by step.

cheers chrys