better use of wxString

Pad edit dialog uses now default layers names in modedit and the current board layers names in board editor

This patch applies on the very last svn  (r2402) and removes all
disfunctionnal python code (including deletion of unused strings)

a common part being defined as have a common value.
This is true for most designs but will produce an
incorrect output if two or more parts with the same
value have different footprints, tolerances, voltage
rating, etc.  Also usefull if the following fields
are edited: 
	FIELD1 - manufacture
	FIELD2 - manufacture part number
	FIELD3 - distributor part number
Check in code for now, doc later.

(non consistent edit pin per pin option and erroneous pin number edition)
Pcbnew: fixing a problem in dialog design rules for small screens (768 pixels height); Better look on bigger screens

* For an obscure reason the focus is lost after loading a board file when starting Pcbnew
* (i.e. only when launching Pcbnew from Kicad or from a command line, with a board filename to load))
* (seems due to the recreation of the layer manager after loading the file)
* This is more a workaround than a fix.

All: fixing a recent problem when using scroll bars: the full screen was redrawn, that can be very slow in Pcbnew.

All: fixing a recent problem when using scroll bars: the full screen was redrawn, that can be very slow in Pcbnew.

* Make USE_WX_ZOOM clipping routine actually clip rather than just test
  if line needs drawn.
* Clean up as many USE_WX_ZOOM #ifdefs as possible.
* Minor coordinate rounding improvements.
* Minor scrolling and panning improvements.
* Remove unused KicadGraphicContext object code.

    1)  nested quotes.  This is in anticipation of broader usage of the
        file type/syntax.  A string like this in the file:
            "my ""favorate"" string"
        can be returned as
            my "favorite" string
    2)  CommentsAsTokens is implemented, so you can ask the lexer to return
        comments as tokens, so they can be preserved.  The default is to ignore
        them.  A comment is defined as any line that has # as its first
        non-blank character.  (This means comments cannot follow anything else
        on a line.)

use size of first element in case the size of an element changes from that of a pointer in the future