[Evolution] New Message Composer - Call for early testers

[Milan Crha <mcrha redhat com>]

        Hello all,
I'd like to let know anyone interested that I've just committed a giant
change in the Evolution's mail composer code, a rewrite to use
JavaScriptCore API instead of the deprecated (since WebKitGTK 2.22) C
DOM API. It makes the work with the composer slightly different,
especially when it comes to the quoted parts editing, but not only
there. The change landed for the upcoming 3.37.2 development release,
thus for the 3.38.0 stable release.

I'd appreciate any early testers, to fix as many bugs as possible
before the 3.38.0 (that's planned for September 16th [1]). Please note
it's a development version, which can contain various bugs, thus if
unsure, then better not try it. 

The changes can be tested in Flatpak, which runs as a separate sandbox,
it doesn't change anything on the host system's installation, thus it's
easy to switch between the development version and the stable version
on the host system. There can be used these steps [2] to build it, just
replace any "-stable" with "-master" (quotes for clarity only) in the
steps. The condensed steps are below [4]. The desktop environment can
prefer the Flatpak version over the system-installed version of
Evolution. If it's not desired, then remove:

   ~/.local/share/flatpak/exports/share/applications/org.gnome.Evolution.desktop

The Flatpak version can be run from a terminal with:

   $ flatpak run org.gnome.Evolution

It can be easily recognized which of the two versions is running, the
composer's common toolbar contains an "Align Justified" button, which
is not available in the current stable version. The Help->About is also
a good place to get the exact version running; it also shows which
commit the sources are at, which is a valuable information as well (see
the Receiving Updates section at [2] or below at [4], with which the
updates can be received before they are released).

You can file the bugs at [3], just make sure you clearly state it's on
the development version. I'm going to close most of the old composer
bugs, due to these giant internal changes. It'll be better to retest
all of them in 3.38 (or with the development version).

        Thanks and bye,
        Milan

[1] https://wiki.gnome.org/ThreePointThirtyseven
[2] https://wiki.gnome.org/Apps/Evolution/Flatpak
[3] https://gitlab.gnome.org/GNOME/evolution/issues/new
[4] The condensed steps to build in Flatpak:

Initial build (this is basically the "Build Evolution" section from [2]):

   $ mkdir ~/flatpak
   $ cd ~/flatpak
   $ wget https://gitlab.gnome.org/GNOME/evolution/raw/master/flatpak/org.gnome.Evolution-master.json
   $ flatpak-builder --force-clean org.gnome.Evolution-master org.gnome.Evolution-master.json && \
     flatpak build-export localrepo org.gnome.Evolution-master && \
     flatpak --user remote-add --no-gpg-verify --if-not-exists evolution-repo localrepo && \
     flatpak --user install evolution-repo org.gnome.Evolution

Receiving Updates:

   $ cd ~/flatpak && \
     flatpak-builder --force-clean org.gnome.Evolution-master org.gnome.Evolution-master.json && \
     flatpak build-export localrepo org.gnome.Evolution-master && \
     flatpak --user update org.gnome.Evolution