Fix flowAppCpp

[JulianGro]

This PR updates flowAppCpp to use local entities instead of the removed 3d overlays.

There are three bugs that I haven't been able to fix (though I don't think they are new):

• Switching avatars while having the debug view open doesn't remove the old debug entities.
• Flow “chains” that are just a single bone instead of a proper chain, will draw a line to 0,0,0 coordinates. On line 470 it goes up the flow chain, but because there is only one bone it hits undefined behaviour. I am just not good enough at JavaScript right now to figure out how to properly check against that.
• The joint selection dropdown in the collisions tab doesn't work. The joints are in there, as selecting the box, moving with the arrow keys, and pressing enter, changes the selected joint. The dropdown itself just doesn't seem to appear.

[Colorfingers]

Code looks good to me... no breaking changes from what I can tell...

[ksuprynowicz]

Everything looks fine :)