others minor bugs fix.

pcbnew Rewrite the GUI relative to the tracks widths and vias diameters and drills selection and edition, for compatibility with new netclass approach.

See also changelog

* Create single event handler for grid size events.
* Fix all frame windows to use new grid size event handler.
* Use offset relative to ID instead of ComboBox index to save last grid size.
* Move last grid size load/save setting into WinEDA_DrawFrame.
* Add equality and assignment operators the GRID_TYPE.
* Add current grid helper methods to BASE_SCREEN.
* Add GetPins helper to LIB_COMPONENT to replace GetNextPin where applicable.
* Add AppendMsgPanel helper to WinEDA_DrawFrame.
* Improve rounding for display of coordinates when millimeter units are selected.

Fixed problems in libedit and crashes when no component loaded

* Split out application specific command IDs to prevent unnecessary rebuilding.
* Eliminate duplicate menu and tool bar command IDs.
* Split component library editor and viewer definitions to separate header files.
* More component library and document file merge code.
* A bunch of minor string readability and consistency fixes.

pcbnew: Starting work on undo/redo in pcbnew. Only some delete item commands are stored in undo/redo stack

* Applied sheet reference plotting patch from Lorenzo.
* Fixed bug in Pcbnew plot dialog, ignore user scaling when controls are disabled.

Minor others changes.