Added REASON enum for Reset() function, so tools will know why a reset occured.
Fixed SELECTION_TOOL (it was bailing out, when a new board was loaded and some items were still selected).
Added removal of VIEW_ITEM groups after changing layers and removing items.

Fixes the case, when waste is never greater then the worst case and seeds assignment does not occur.

template<> -> template <>
Some more reformatting according to uncrustify results.

Added typedefs for VIEW_GROUP iterators. Fixed improper order of layer drawing for VIEW_GROUP items.

VIEW_GROUP now does not change depth during drawing. Introduced functions for manipulating stored items.
FIxed problem of overlay being covered by other layers while panning.
Few minor fixes.

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.

More effective way of updating bounding boxes. IsCached() method made public. Removed some of unused fields from the layer description structure.

VIEW_ITEMs save the layer numbers they use, it allowed to speed up removal of items.