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

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.

Added rotate & flip to the pcbnew.InteractiveMove tool, hotkeys for them and undoing all the  operations on cancelling the tool.

Removed TA_ActivateTool (now tools are invoked by sending TA_Action event, with the tool name as string parameter).
Developed TOOL_Action class & added ActionManager. Hot keys registered by tools are processed.
Selection & move tool can be invoked by a hot key.

Fix minor bugs in cleanup dialog options and plot solder mask function (thanks to Lorenzo to locate these bugs)