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.

Less objects are allocated dynamically.
CONTEXT_MENU is being run using its copy (it saves a hassle of following the lifetime of object).

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

FIxed TOOL_EVENT::Modifier() (now it returns value for current modifier, not only if there is one active or not).

Pcbnew: better dialogs to select the active layer or a layer pair. Add an option (hotkey+popup menu) to place a via and select the new active layer
(useful for boards having more than 2 layers)
Eeschema:fix compatibility with old schematic files, when they  contain ERC markers.
Pcbnew: better test for allowed layers when creating/editing Dimensions and some other Graphic items
Drc:  fix comments and messages for some drc tests.
Fix minor bugs in cleanup dialog options and plot solder mask function (thanks to Lorenzo to locate these bugs)

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.