Implement Community Presets

[Digitalone1]

This is a almost complete implementation of the Community Presets #2445.

What has been done:

• local presets are not sorted by C++ anymore (this is not needed because we already have the GtkSorter)
• also the removal of duplicates for local presets has been removed (this was intended for multiple path, but now we have only one folder for local presets, so no need to check for duplicates)
• added string vector properties which contains the directories where community presets may be contained (these are derived by the xdg data directories)
• added some utils to scan the above mentioned directories in order to track the community presets
• added an AdwStack to the presets menu popover which splits the view between the local and the community presets
• added a ListView to the community presets stack which tracks the presets by full path, so same presets in different folders can still be seen ad different items
• implemented an util which uses regex functions to extract the package and the preset name using the full path
• implemented functions to load a community preset without importing it (just to test how it sounds)
• implemented functions to import a community preset info the local path in order to be shown into the local presets list
• SYSTEM_DIRS constants in meson.build have been removed since they were unused
• changed the initial directory for opening dialogs; now it's the home directory (it works now and it's intended to be the starting point for importing presets/irs/models...)
• tried to implement a GtkExpression to filter the community presets when making a search, but it's not working
• added an overlay to show a status page in case the community presets list is empty, but it's only a draft, this has to be completed

[github-actions]

Workflow failed, but the following artifacts are still available for this pull request:

• easyeffects-archlinux-merge-b41fce706-into-27c4f544f-x86_64.zip
• easyeffects-flatpak-merge-b41fce706-into-27c4f544f-x86_64.zip