* dock: add trash bin button
- icon reflects content- filled/empty
- multiple file manager support with nautilus as default, builtin as
fallback
- settingsspec at dock tab
- context menu
* fix: remove support for builtin filebrowser
needs specific adaptors at FB adhering the trash freedesktop spec
* fix: suppress auto-hide dock with trash context menu open
* feat: allow for custom file manager command
* feat: switch runner to proc.runcommand with toasts on command failures
