Refactor input mouse handling

[philippotto]

At the moment, we are manually attaching to a dom node via a selector, which can change (e.g., when the golden layout adapter re-instantiates the layout) though.

[daniel-wer]

This is partly resolved in #4031.
Components which still break because of this (but lower prio):

• HammerJS touch handling (as hammerjs doesn't seem to support event delegation, but we can probably imitate it)
• ThreeJS Trackball Controls, i.e. the right click rotation

[philippotto]

See https://github.com/scalableminds/webknossos/pull/5429/files#r621310352 which again gave some attention to this issue. The new FlexLayout lazily renders the input-catchers (so, if the viewport is hidden by the layout it won't be rendered at all). Since we are waiting for these DOM elements, the current approach is a bit sub-optimal (perf-wise and also in general a bit messy).