Expose BeehaveTree graph view in editor's bottom panel

[NectoT]

Is your feature request related to a problem? Please describe.
Visualising your behaviour tree helps with analyzing and fixing your logic and code, and so it would be nice to have a quick and easy access to an already made feature without having to launch the game

Describe the solution you'd like
A tab with the BeehaveTree graph view in the bottom panel that appears when a BeehaveTree node is selected in, similar to how AnimationTree and AnimationPlayer UIs work right now. Here's a working example of the idea: 650f300

Describe alternatives you've considered
An already existing debug view can certainly be used, but with the overhead of launching the game and having to restart it with every behaviour tree change.