Simplify interactions with editor tools

[willnationsdev]

I would like to be able to quickly and easily find and interact with tool scripts. The "find" part can easily be achieved by creating a "Tool" CheckButton in the dock that is automatically toggled off and disabled when in tabs other than the Script tab.

For "interacting", there are two scenarios. One is regular nodes that we've created marked as tool (in which case we'll be wanting to extend or instance them like any other node), and the other type is EditorScript which I would like to be able to execute directly from the Script tab (perhaps put a "play" button beside it in the TreeItem that only EditorScript scripts have).

I'll need to officially version this plugin prior to adding this feature though because implementing this functionality would require exposing "run an editor script" functionality to the EditorPlugin class. It would be a feature only compatible with later versions of the engine. As such, I can't add this feature until the memory leak bug (#11) is fixed and an official version is setup.

As an alternative, what people can currently do is type in EditorScript into the "filter by class" filter, double click the script to open it, and then hit Ctrl+Shift+X with the Script Editor open in order to run the opened EditorScript (slightly more cumbersome).