Use libhandy Hdy.ViewSwitcher instead of Gtk.StackSwitcher

This commit also adds libhandy as a dependency.

This is a part of the View-Switcher-Initative.
More information: GNOME/Initiatives#16
Status Job ID Name Coverage
  Test
failed #736061
fedora

00:02:32

passed #736062
flatpak
flatpak

00:01:50

 
  Review
skipped #736063
review
skipped #736064
allowed to fail manual
stop_review
 
Name Stage Failure
failed
fedora Test
meson.build:56:0: ERROR: Dependency "libhandy-1" not found, tried pkgconfig

A full log can be found at /builds/haecker-felix/d-feet/_build/meson-logs/meson-log.txt
Running after_script
Uploading artifacts for failed job
Uploading artifacts...
WARNING: /builds/haecker-felix/d-feet/_build/meson-logs/testlog.txt: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1