bulk improvements for selection and edit tools (GAL) disambiguatin heuristics and smarter grid alignment

Introduced SELECTION_CONDITIONS to determine which menu entries should be visible in the SELECTION_TOOL context menu, depending on the selection.

Removed TOOL_ACTIONs: selectionSingle, selectionClear. SELECTION_TOOL methods are called directly instead.

Added preference for selecting tracks/vias/graphics if there is a module present in the selection point.

TOOL_EVENT message is supposed to contain string as parameter.
Added missing header for class_drawsegment.h (KiROUND).
Renamed SELECTION_TOOL::containsSelected() to SELECTION_TOOL::selectionContains().

- pcbnew.InteractiveSelection.Single for selecting a single item
- pcbnew.InteractiveSelection.Clear for clearing the selection
Made SELECTION_TOOL::clearSelection private.

SELECTION_TOOL::SELECTION::Clear made private, as there was no chance to call it outside the SELECTION_TOOL class.

Modifications done using the EDIT_TOOL are saved using the default KiCad's undo buffer.
If there is only one item selected, info about the item is displayed in the bottom status bar.

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.

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

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

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.

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.