More action stuff

Some more work on actions:
- Add first selected file display name token
- Add parent display name token
- Unify string expansion across exec, label, tooltip
- Add separator definition for exec file list
- Add quote type for exec file list (single, double, backtick)
- Add action dependencies (searches for file in path)
- Add conditions - 'desktop', 'removable', gsettings boolean key, dbus name
- Added mailto actions, removed hardcoded stuff.
- Added New Launcher action, removed hardcoded stuff (depend on https://github.com/linuxmint/Cinnamon/pull/2333)
- Added Add Desklet, Change Background, Set as Wallpaper actions, removed hardcoded stuff
- Added "nodirs" to extensions options.
- Added ability to show actions in places sidebar and treeview sidebar
- Added action manager to consolidate action management code for use in views, treeview sidebar, places sidebar

- Added translation scripts to extract strings from .nemo_action files, get them gathered in potfile, then merge translations once new .mo files are installed to system.