CMakeLists.txt options to build scripting or scripting modules

It does nothing but loading and initializing right now.

ModEdit (and ModView): make "invisible" texts visible. They are not visible in  the board editor, but must be visible in the footprint editor.
Minor doc update.

* Convert Eeschema from manually linked list to DLIST for storing
  SCH_ITEM objects.
* Add helper functions to SCH_SCREEN for appending list of SCH_ITEM
  objects.
* Fix bug in wire editing code for accurate undo/redo behavior.
* Add member to DLIST to append another DLIST.
* Other minor code cleaning.

Pcbnew: zone filling: fix broken thermal relief shape for oval pads. mainly noticeable for oval pads having very different X and Y sizes.

* Pcbnew: in hight contrast mode the 'V' hotkey did not always refresh the screen.
* Eeschema: incorrect print scale when the option 'Show page limits' is disable.

    derived classes' implementations of these functions become non virtual and
    can be truly _inlined_ for speed!  All GetPosition() in derived classes were also
    changed to return const wxPoint&, that is, a reference rather than a
    full copy of the position wxPoint. There was no need for polymorphism in
    {Get,Set}Position() since we never call these functions via generic pointer.
  * Remove BOARD::{Get,Set}Position() since they were only there to satisfy
    the pure virtuals established in BOARD_ITEM, which are now gone.
  * Added const wxPoint& CPolyLine::GetPos(), made CPolyLine::Get{X,Y}() inline.
  * Derive CPolyPt from wxPoint so we can return "const wxPoint&" fromt
    CPolyLine::GetPos().

Eeschema: Viewlib is now accessible from Libedit (to browse libs or load a component to edit)
Libedit: uses now the same dialog as the schematic editor to load a component
Some code cleaning.

    which is in turn already within BOARD.
  * encapsulate class D_PAD with accessors, making data private.
  * make D_PAD::GetBoundingRadius() do its longer calculation lazily, based on
    m_boundingRadius == -1.

Design rules: increase number of vias and tracks sizes
Pcbnew: netlist reader: change from my recent commits to keep netnames in pads for footprints not in netlist
(allow an user to place some footprints by hand, set pads netnames and do not lost these netnames when loading a netlsit)
Fix other very minor issues.

Code cleaning and other minor fixes.

the match between wxString::Format() or wxString::Printf() format strings
with passed arguments, but does this at runtime, not compile time.
Fix some mismatches.  size_t is a 64 bit type on x86_64 whereas int and
unsigned are 32 bit types.  On 32 bit machines they are all 32 bits so
this error is probably not triggered.