KICAD_PLUGIN::Load() is solid now, except for missing globals, which
still need to get moved into the class BOARD.

Same for KICAD_PLUGIN::Save(), only missing globals, which once they
are in the BOARD class, will be added.

Pcbnew: fix issue when creating new tracks: sometimes a ratsnest remains active although a track exists.

  * changed all the RotatePoint() functions in trigo.{h,cpp} to take a double as the
    angle, which is still in tenths of degrees for now.
  * EDA_TEXT::m_Orient is now double, still in tenths of degrees (for a short while),
    but the double means parsing files and saving them use a different format string.
++pcbnew
  * DRAWSEGMENT::GetStart() and GetEnd() do not operate for S_ARC like they used to.
    They are now simply accessors for m_Start and m_End.  Use DRAWSEGMENT::GetArcStart()
    and GetArcEnd() and GetCenter() for arcs.  specctra_export.cpp was the only
    source file dependent on the old behavior.
  * DIMENSION::m_Text is now contained, not dynamically allocated.
  * more kicad_plugin work.

* Enable replace toolbar button and menu entry.
* Improve find replace logging granularity.
* Fix find and replace dialog control hiding and disabling.
* Minor improvements to the SCH_FIND_REPLACE_DATA object.
* Move find collector list iterator into the collector object.
* Add visibility override flag to EDA_ITEM to temporarily show items that
  are hidden during find and replace.

  * added BOARD::GetPad(int), made BOARD::m_NetInfo private, and contained
    within the BOARD, not dynamically allocated and owned via pointer.
  * added BOARD::GetPadCount()
  * changed NETINFO_LIST::GetCount() to GetNetCount()
  * added BOARD::GetNetCount()
  * more kicad_plugin work.

Pcbnew: fix bad initialization of default track width and vias sizes when starting pcbnew with no board loaded.

 * Fix compil issue about automatically created pcb_plot_params.h :
     pcb_plot_params.* moved from pcbnew to common because item_io.cpp (using this file) is compiled in common.

In common.cpp GetTimeStamp is renamed GetNewTimeStamp (a better name).
Pcbnew: prepare work to calculate connections between pads that inteserct and therefore can be connected without any track (composite pads).

which should eventually go away in favor of kicad_plugin.cpp.
Add CMake options USE_NEW_PCBNEW_LOAD and USE_NEW_PCBNEW_SAVE, which should not be
used yet, and both default to OFF accordingly.