Make Drawing Tool totally independent from UI buttons

[#77436188]

WIP: there are no buttons at the moment at all.
Refactor event system (use EventEmitter2 lib)

[#77436188]
Fix delete tool (keyboard support)
Implement simple jQuery longPress plugin

[#77436188]
Implement new UI classes - Button, Palette, UIManager

[#77436188]
Provide UI definition (ui/ui-definition.js) and use new UI system

[#77436188]
Remove btn-group.js

[#77436188]
Remove ColorTool, move similar functionality to drawing tool API

[#77436188]
Implement stroke color palette - ColorButton, StrokeButton, etc.

[#77436188]

WIP
Implement new stroke color UI

[#77436188]
Implement new fill color UI

[#77436188]
Fix palettes show / hide + small refactoring of UI definition

[#77436188]