Don't recreate backgrounds all the time

Based on @marty1885 's work in !531 (merged) i removed the recreating of backgrounds by listening to PhoshMonitor::configured and PhoshShell::notify::primary-monitor. This also includes the suggested cleanup of PhoshBackground as suggested by @sebastian.krzyszkowiak in !531 (merged). Since we wait for the final configure i don't think we need !541 (closed).

This way we make sure PhoshBackground only needs minimal knowledge about what's going on with PhoshMonitor and ideally we remove the phosh_shell_get_usable_area () at one point as well so this class an focus on rendering the background.

Closes: #325 (closed)

changed the description

mentioned in merge request !551 (merged)

mentioned in merge request !541 (closed)

added 3 commits

• e15230e6 - background: Skip image loading when using colored mode
• 5e56df63 - build: Move meson to test-lib
• 7c30e37b - tests: Add a simple background test

Compare with previous version

added a test now that we can do so easily

Looks good, thanks!

merged