Software tools and custom panel items rework

[JosefNemec]

More and more people request option to add custom items to Sidebar, Top panel and Tray menu (and other places). Current "software tools" feature allow these items to be added to Sidebar, but it's not very flexible solution.

This issue is about getting rid of Software tools and implementing more general way of specific general actions that could be placed and executed from various parts of the application. Basically speaking, software tools should be replaced with something similar to how game actions currently work, just on global scope.

Specific action would allow to specify:

• What to launch. Executable, URL, script.
  • Also ability to execute various application actions, like starting specific game, applying filter preset etc.
• Icon, description and some other visual related things
• Where this action is executable from. Sidebar, Top panel, Tray menu etc.
• Option for nested actions and folders???
• Some way to set order of these actions.

Current SDK support for adding new items to Sidebar and Top panel should be unified/adjusted to this system.

This will be supported by both Fullscreen and Desktop modes.

Comment in #2556 also mentioned support for menu items, but I think that should be probably handled differently since menu may require specific context, like selected game. But I'm open to suggestions.

Related #1669 #1869 #2556 #2368 #2367

[trymeouteh]

Would be amazing to be able to choose what software tools are installed or not with a checkbox setting and to be able to access software tools in fullscreen mode.

[hasinabrar1996]

HOW TO DO THAT???