This attempts to solve bug
[#714921](https://bugzilla.gnome.org/show_bug.cgi?id=714921).
They are available as two buttons on the format bar, next to font
options. The icons I used are taken from a free icons site just for demo
purposes and should be replaced by new icons. Also I did not include
hotkeys mainly because I could not come up with a good one, also they
are pretty uncommon I think.
Also added new icons to icons/CMakeLists.txt
Some remarks:
* Note that Meson adds a hard dependency on Python 3.
* All dependencies and defines are now listed together.
* Some build files were put in their respective subdirectories, e.g. the Geary
engine library will be built from the Meson file in `src/engine`.
* `--fatal-warnings` is no longer an explicit flag, as Meson provides
`-Dwerror=true` for this.
* An explicit resource file needs to be used. The issue to support this from
Meson itself can be found at https://github.com/mesonbuild/meson/issues/706 .
* The `gnome.yelp()` function parses a LINGUAS file so we no longer need to keep
track of all languages in our build system.
* There are no Debian scripts defined in the meson.build files to keep them
clean, but they can be kept as separate scripts in `build-aux`.
* Left out the `dist` target as there is now `ninja dist`
* `geary-docs` is disabled by default, as valadoc-0.38.3 returns errors.
https://bugzilla.gnome.org/show_bug.cgi?id=777044
Themes may change the app icon, which would also change the draft folder
icon in Geary. Import Adawaita's to match current use, install, use, and
update copyright.
When implementing bug 765359, it appears that Geary is doing too much
work to load icons. Simplify it a bit.
* src/client/components/icon-factory.vala (IconFactory): Don't bother
loading an application icon, it's easier and works better to just use
an icon name where needed. Don't bother adding all of the icons/*x*
directories to the icon theme search path, just make the icon's
directory hierarchy follow the XDG/hicolor spec and add the base
directory. Remove now-redundant code.
* src/client/application/geary-controller.vala: Set the default icon name
for all geary windows.
(GearyController:on_about()): Set the name for the icon in the About
dialog.
* src/client/components/main-window.vala (ApplicationWindow): Don't
bother loading icons for the window, just use the new default.
* src/client/notification/libnotify.vala: Don't bother passing the
application icon through for error notifications, an icon name has
already been set.
* icons/*x*/geary.png: Move to a new directory hierarchy that follows the
hicolor spec.
* icons/CMakeLists.txt: Updated to use new paths to the icons.
Better icon courtesy Daniel Fore. Also increased the size of the
toolbar and reduced the child spacing in the composer to better
utilize space. This might also handle #5054, but need to confirm
separately.
