Remove prototypes of non-existing callbacks
Don't export callbacks not used from Glade
Normalize callbacks prototypes
Move Glade-only callbacks out of callbacks.h

There is no need to expose the Glade-only callbacks in the header as
nobody uses them directly anyway;  and not having them makes the header
a little less bloated.
Remove redundant toolbar-specific callbacks
Add two missing Glade-only prototypes
Use the appropriate prototype for the window's delete-event callback
Don't manually connect handlers Glade can connect for us

Don't bother manually connecting handlers that Glade can connect for us
just as well.
Move on_clone1_activate() to callbacks.c
Fix build warning about missing return value.
Callbacks: get rid of the ugly `insert_callback_from_menu` global
Move include insert callbacks to the UI code where they belong
Move date insert callbacks to the UI code where they belong
Make sure the current document is still the same after Save All

Save All updates the sidebar and title bar with the document that was
the current one when the action was triggered, but the action could
have changed the focused document if an non-file-backed file required
saving.  So, make sure current document is the same after the action.
Remove some dead code
Remove line number zoom hack as it is no longer necessary

Since cbf9813632d7ee921ffa1fda0d1f69128b2bc755 we have a proper
solution for maintaining line number consistent with the editor zoom,
so drop the old hack.

This also allows to remove the now useless third argument of
sci_set_line_numbers().
Merge branch 'callbacks-cleanup'
main: Refactor quit functions

Move quit-related functions to main.c and make them static. main_quit() now
does all the heavy work and can be called from signal handlers.
actions: Introduce GtkAction for each keybinding.

For all existing keybindgs a GtkAction is generated with a (for now)
empty callback. All of this is autogenerated.

From now on, keybindings can be ported over to GtkAction one by one.
actions: ui_utils: Load GtkActions via GtkBuilder.

With the GtkActions being specified in Glade they have to be loaded by
GtkBuilder. A workaround for a Gtk bug (fixed in 3.6 and newer) is needed to
make default accelerators work.