autostart: added new setting autostart-ignore.

It's a string array that needs to be populated with the eventual *.desktop file names* to ignore during startup.
vera: added an OptionContext to parse command-line arguments.

Currently --enable-autostart, --disable-autostart and --plugins(-p) are supported.
vera: added the GTK+ option group to the OptionContext.
src/Recipe: ensure we embed the soname in the library.

This means that we can actually get a working Debian package.
0.22
Merge branch 'master' into debian
0.22-1