Add config tweaks to define colors used in updater

Useful in case (default) colors do not work well with the theme.
Closes #12.
conf: Fix parsing ColorXXXX re: #rgb syntax

Because our parser treats '#' as a comment marker, we can't use the exact
same syntax as GdkRGBA, so instead a dot shall be used.
conf: Fix saving ColorXXXX re: #rgb syntax
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.
Fix wrong package name used on button

In case of conflict, we always keep pkg1, and the question is whether we
remove or keep pkg2.
Use $XDG_CONFIG_HOME instead of $HOME/.config

Likely to not change what's actually used, since it'll default to the same
value should $XDG_CONFIG_HOME not be set, but it's better/proper/allows
user customization.
small confusing-at-first typo in README.md
Merge branch 'patch-1' of https://github.com/emanueLczirai/kalu into next
README: Fix typo
Force icon size on notifications

Since GTK+3.14 the icon size might not be the requested one, so force it
if necessary.
Fix handling clicks on systray icon

The button-press signal wasn't marked handled when it should have.

(Somehow with GTK+3.14 this could lead to middle clicks be processed
twice, though I'm not sure why.)
Remove useless code

Leftover from changes in 7ee7ef77
Add a 16x16 logo for use in menus/buttons

Because GTK+3.14 won't resize the 48x48 one anymore, and gives us extra
large icons on menus/buttons instead.

Fixes #20
Minor fix handling dbl-click on systray icon

Use gtk-double-click-time instead of hardcoded (default of) 250ms.
Minor tweak

Don't process click in the off chance the source was destroyed already.