Add button to remove bit-ecs entities

[keianhzo]

I find the ecsDebug panel pretty useful while debugging components, I just missed a way to easily remove a bit-ecs entity to test exit cases. This PRs adds such a button to the object properties panel.

[netpro2k]

This seems like a useful debug tool. Note that the user-facing way to delete a spawned entity (something you paste in or upload) is hovering over it and pushing the X key. Obviously we need to make that more discoverable (probably y implementing the handler for the button in the object menu)

[johnshaughnessy]

RE "Implement the handler for the button in the object menu"

I've done this in another commit (unfortunately part of an unrelated PR): 02b9a4d

[keianhzo]

I wasn't aware of that shortcut in the new loader. It seems to work for spawned nodes from the media toolbar but not from the chat. For testing the new bit-ecs components I was using mostly the chat command that's why this remove button.