Renamed BOARD_CONNECTED_ITEM::SetNet() -> SetNetCode()
Added BOARD_CONNECTED_ITEM::GetNet() for accessing NETINFO_ITEM* of a given item.
Fixed module editor crash when launched to edit a module from a PCB.
Replaced some BOARD::FindNet( item->GetNet() ) calls with BOARD_CONNECTED_ITEM::GetNet().

Pcbnew: fix bug #1272714 . Code cleanup: use 2 different enums for pad shapes and pad drill shapes. Remove never used pad shape.

NETINFO_ITEMs are not stored in a vector anymore, instead they are held in a unordered_map. Now, the net codes may be not consecutive. There is another way for assigning net codes (using a static int that holds a possible empty net code and a function that makes sure it is not used [getFreeNetCode()]).
Removed some unused fields (NETINFO_ITEM::m_NbNodes, m_NbLink, m_NbNoconn, m_Flag).

D_PAD::GetNetname() and D_PAD::GetShortNetname() were moved to BOARD_CONNECTED_ITEM. Now they use the net name stored in NETINFO_ITEM.
Moved some one-line functions from class_board_connected_item.cpp to class_board_connected_item.h.
Added a copyright notice, moved Doxygen comments from class_board_connected_item.cpp to class_board_connected_item.h.

I have some doubts if changes introduced pcbnew/dialogs/dialog_pad_properties.cpp do not break anything, but I could not find a test case that breaks the pcbnew.

Performed tests:
- changed pad's net name from empty to existent - ok, name was changed
- changed pad's net name from empty to nonexistent - ok, error message is displayed, net name stays empty
- changed pad's net name from existent to empty - ok, net name became empty
- changed pad's net name from existent to nonexistent - ok, error message is displayed, net name is not changed
- (re)reading netlists, including net changes - fine, changes are applied, but empty nets are still kept
- loaded pcbnew/pcad2kicadpcb_plugin/examples/CK1202_V1.pcb to test P-CAD import plugin - ok, net names are correct
- imported an Eagle 6.0 board (Arduino Uno; http://arduino.cc/en/uploads/Main/arduino_Uno_Rev3-02-TH.zip) then saved in .kicad_pcb format and reloaded - ok, net names are correct
- saved demos/video/video.kicad_pcb in legacy format and then loaded it again - ok, net names are correct

More layer classification cleanup

* Complete encapsulation of the MODULE class.
* Complete encapsulation of the EDA_TEXT class.
* Encapsulate most of the ZONE_CONTAINER class.
* Add pcbcommon library as a dependency for reSWIGging the scripting
  support.  This should cover most dependency cases.

Pcbnew: Partial merge from pcad2kicad (from Alexander Lunev). Fix an old bug related to pads with offset: sometimes the connection to a zone was not detected.

* Improve the stable and testing build version option logic.
* Use CMake FindPythonInterp to configure the Python interpreter.
* Use Python interpreter to determine the system Python module install
  path if not already defined on the command line.
* Add header symbol checks for asinh(), acosh(), and atanh().
* Add test source to check for isinf() which can be defined as a C++template.
* Replace conditional compile on windows systems for aXXXh() with CMake
  configuration tests.
* A few minor MSVC compile fixes.
* Fix incorrect python environment string in fixswigimports.py
* Create a separate document for KiCad CMake build options.
* Create a separate how to compile KiCad on Windows document.

Pcbnew: Add pcad2kicad pcb plugin, to import PCAD boards ( .pcb ASCII data file PCad 2000 format ) from Alexander Lunef