Improved grid, more shortcuts + redesign of some areas

[MoritzBrueckner]

Depends on https://github.com/armory3d/zui/pull/92 and https://github.com/armory3d/zui/pull/91

This is a huge PR, the commits are a little bit messy, sorry about that.

A lot of things are new/improved:

• Element handles remain highlighted during editing, even if the mouse is not hovering them anymore
• Grid is fixed and there is support for absolute and relative grid (+ respective settings) It works the following way: If you press Ctrl, the grid setting will be inverted (like in Blender). If you press Alt and the grid is on, the relative grid setting is toggled. Absolute grid means that the position or size will adjust to the grid you see on the canvas, relative means that the grid is relative from the original position of the transformation.
• Realtime grid preview
• Shift now toggles slow movement, like in Blender. Doesn't work for rotation.
• Shortcuts are now stored as keycodes, based on new KeyCode element (https://github.com/armory3d/zui/pull/92)
• Show current operation in the bottom left corner
• Redesign settings and add element windows
• Allow axis movement (with x and y) for transform editing also when the edit was started with the mouse (grab, drag)

I probably forgot something, but these are the most important changes. Next time I will create more and smaller commits. Sorry :)

It also makes sense to update Kha, because until a few days ago Ctrl + left click wasn't possible until a PR fixed it.

[sh-dave]

just FYI: instead of all the changes in c0a5d37 you could also do a single using zui.Ext; (see static extension)

[luboslenco]

Thanks once again!