This PR changes the overrides system from being based on dropdowns to a drag-drop system.

• The user is presented with a "toolbox" of available evaluatables at the bottom, sorted by category. They are then able to drag and drop these into the canvas rather than having to find the one they want in a single long list.
• The user is also able to drag around already-placed evaluatables to new positions, swapping them over (or holding to Ctrl to copy and overwrite the destination).
• Users can also drag already-placed evaluatables into the toolbox to allow them to save it for future re-use. This feature is replacing the somewhat limited copy-paste system that existed previously. These saved "templates" are stored in the global configuration and are available to any profile (although invalid state variable paths will be reset).
• Thanks to the dropdowns being removed, the decluttered interface is a lot more approchable now and is easier to understand.

From a technical standpoint, the SetApplication method has been removed from the evaluatables, since most did not actually need to use the application context (only the ones that presented the user with the ability to choose a game state variable).

Instead, an inherited attached property has been added which is set at the root level of the override editor. This property is then automatically propogated down to other controls in the logical tree and when a variable picker needs to be used it can access it through this attached property instead. This has fixed issues with manually propogating it, such as #1927.

This PR also adds a new control for allowing picking of game state variables, saving all layers from having to manually populate a dropdown box.

Finally, this PR also adds some new evaluatables:

• A delay (for boolean, number and string) which delays the signal passed to it by a set amount of time.
• A flip-flop boolean evaluatable, which takes two booleans 'set' and 'reset'. When set is true, the flip-flip will start outputting true until the reset becomes true. This can be used as a basic togglable gate, for example making some keys light up when the A key is pressed and then turn off only when the B key is next pressed.