Read plugin config from a file

[Iago Toral Quiroga <itoral igalia com>]

Hi,

I'd like to work on fixing bug #636064, it is a feature request to add
the possibility to load plugin configuration from a file.

Given that different apps may need different configurations for the
plugins (example: each app has to use its own API keys), the way this
would work is that each app ships the config files for the plugins.

One option for the file format is a key-file, which is standard, easy to
use and fast to parse (GLib as you know supports this already). That
would work good for almost all the use cases I can think of. 

There are a few situations where this may not be enough though. One
example would be a plugin which accepts configuration for its own
content structure (this is something we discussed on IRC for a Tracker
plugin for example).

I guess for cases like this an entry in the key-file which value is the
path of another file with the content structure definition is a good way
to go and would also help to separate straight forward plugin
configuration from more complex stuff like the content definition.

Opinions?