revamp project assistant dialog

Use AdwWindow instead of deprecated GtkDialog, and GtkFileDialog
instead of deprecated GtkFileChooserNative.

Requires libadwaita >= 1.4

use N_() instead of __() to mark translatables

optimization: cache visible automation tracks

port some more deprecated Gtk widgets

remove unused RulerMarker code

export dialog: port GtkTreeView to GtkColumnView

fix header widget being focusable

stop using deprecated gtk_style_context_lookup_color()

fix various gtk depreciations

remove unused widget code

change audio effect icon in plugin browser

show focus ring on all focusable widgets

refactor channel send selector (use GtkListView)

cpu widget: add/remove sources on map/unmap (fixes crash), re-enable tooltip

implement cycling focus through panels with F6 and jumping to top with F10

move code from accel.c to zrythm_app.c

add focus ring on various widgets, make channel slot themable

fix allocating memory in dsp threads when recording automation

Also make the logic faster by reducing searches.

build: build some external projects with full optimization

remove height requirement for channel plugin slots/sends expanders