Pcbnew :added option to show/hide footprints values and/or references

Removed old color and visiblity dialog
work in progress.
See also TODO, P0)

    * in variable names, change non existent word Hight to High
    * Remove redundant tool in left toolbar (option toolbar)
      (this option is now in layers manager)
    * Show layers in horizontal combo box in same order as in layer manager.
++all:
    minor code cleaning.

fixed minor problems and fixed Layer Alignment Target bug.

patch for relative paths.

Code cleaning.
Patch for 3D problem with macOSX

files cleaning

Fixed others minor problems 

enhancement in Gerbview: page limits can be now displayed on screen. Useful when printing a Gerber layer

But needs wxWidgets >= 2.8.8

fixed some problems in gencad export (not all)
fixed a size problem when opening dialog_layers_setup2 (windows specific)

See also changelog