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

Added error messages for OpenGL framebuffer errors. This should eliminate quiet segfaults in case of drivers that cannot handle multiple attachment points for framebuffers.

Moved VIEW_GROUP creation to the selection tool. In this way selected items are always drawn on overlay, not only when dragged.

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.

Added Init() to TOOL_INTERACTIVE, allowing to set up things that are needed to be initialized only once.
TOOL_ACTIONs can be run from CONTEXT_MENU after adding them.
Move tool actions are available to be run from CONTEXT_MENU displayed after right mouse button click on selected items.
Added some asserts to check the code.