Utils: Simplify initActions

Rename initActions to addActions (showing that the util calls add_action
in the end) and make it less boilerplaty to use.

https://bugzilla.gnome.org/show_bug.cgi?id=739933
Utils: Move accel setup into addActions

Setting upp accelerators (keybindings) inside addActions feels more
natural since you're already working with setting up the actions there
to begin with.

https://bugzilla.gnome.org/show_bug.cgi?id=739933