Add repo name

Repo name is now featured in a column on kalu updater, as well as available
via $REPO in package template for updates & watched packages.
Little fix

Couple functions are callbacks from sources (GSourceFunc) and as such
need to return a gboolean.

Shouldn't have caused issues since the source is destroyed anyways, but
still.
doc: Mention the wait & re-check after system/AUR cmdline
simulation: Show ALPM log messages (e.g. warnings, etc)
prefs: Unchecking a template field wasn't always remembered

When unchecking a template field (to have it use its fallback value) it
wouldn't be remembered when said field has a hard-coded default value
in kalu, which would then be restored. (E.g. the Title field for packages
not found in the AUR)

Now such fields are saved to the .conf file without a value (e.g. "Title=")
to preserve their disabled/falling-back state.

Fixes #17
Add KDE's StatusNotifierItem support

With Plasma Next KDE doesn't support the good old xembed systray, and so
GtkStatusIcon are "useless."

Adding a new configure option --enable-status-notifier to enable support
of KDE's interface via our small library, statusnotifier.

When used, kalu will try to register a StatusNotifierItem first. If it
fails, it will fallback to using the systray.