Changed VIEW::PrepareTargets() to more appropriate name VIEW::ClearTargets(). Added SELECTION layer to always-on-top list.

Mouse movement events are sent during autopanning, as the cursor position changes in the world coordinates (even if it stays still in the screen coordinates). It allows tools to update their state, as if the mouse was moved.

Redraws can be requested way too often than it is required. This commit adds redraw timeout:
- if the view became dirty and there has been no redraw for longer than certain time, it is redrawed immediately
- otherwise, we wait for the next frame

This in general improves smoothness of rendering.

Used in highlighting/routing code.

Removed selection disambiguation in case when there is a choice between a footprint and a smaller component (smaller components have priority).

Changed lifetime of RENDER_SETTINGS (now they are accessible right after PAINTER object is created).

PCB items are refreshed on GAL switching (changes made using default renderer are displayed by GAL).