Selection clearing is invoked using TOOL_ACTION object rather than its name.

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().

Removed a few RecacheAllItems() calls, some of them changed to specific type recaching (using TYPE_COLLECTOR & VIEW_ITEM::ViewUpdate() ).
Removed OPENGL_GAL::SetStrokeColor().

Eeschema:  * Preselect the currently chosen component in the browser when pressing the thumbnail view.
* Various smallish documentation updates in the component chooser area.

- VIEW_ITEM::ViewUpdate() does not update items immediately. Now it marks them to be updated and the real update occurs on the next rendering frame.
- VIEW::InvalidateItem() made private.
- VIEW_LAYER::enabled -> visible
- Some functions moved to header files.

* Allow to select units in components that have more than one right in the
  component chooser dialog.
* Keep chosen unit in history.
* Show preview of current component unit as thumbnail image next to the
  description box.
* Fixes lp:1280567

Changed PCB_EDIT_FRAME::setTopLayer() to PCB_EDIT_FRAME::SetTopLayer() and changed to public (as it had exactly the same functionality).

* Apply Henner Zeller's patch to add connecting line from reference and labels to component position whilst moving to help identify which component the reference or label belongs too

Add a workaround to fix a new bug in wxWidgets 3.0 ( Windows specific ) which shows icons only with a size = 16x16 in menus which have attribute wxITEM_CHECK

Fix some incorrect icons (which were using a not supported font for texts). Add ps_router icon from Konstantin Baranovskiy.

Removed an unnecessary header from class_board_item.h.

Moved netnames (GAL specific layers) to a separate enum, to avoid saving/reading their settings from files.
Added a check for the number of PCB_VISIBLE elements.
Worksheet & general purpose overlay layers are visible by default.

Changed BOARD_DESIGN_SETTINGS::m_VisibleElements from int to long, to assure at least 32 bits length (without depending on the platfrom int size).