Fixed bugs 2965646 (Canceling text operation hides text) and 2959930 (Pcbnew inconsistent Layer names sequence)

- in bloc delete, *do not delete* reference and value fields, that must always exits.
- in block copy *do not duplicate* fields that must be unique for the whole component.

Updated denis dupeyron email address

default is Edit pin per pin for components with parts locked and coupling pin for others.

  * DSNLEXER now owns an abstract LINE_READER by pointer so that polymorphism
    can be used in alternative LINE_READERS.
  * Write FILE_LINE_READER and STRING_LINE_READER.  The latter can be used
    to parse text coming from the clipboard or other string source.

This paves the way for other kinds of LINE_READERs, such as one which reads from a
multiline string which comes from the clipboard. 

Will still need to:
1) add new additional DSN_LEXER constructor,
2) virtualize the LINE_READER's ReadLine() function
3) create derived class from LINE_READER.

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