* Create new dialog to edit environment variables.
* Add helper class ENV_VAR_ITEM to manage environment variable values and
if they were defined externally.
* A path configuration dialog access to KiCad, CvPcb, Pcbnew, and Footprint Editor
window menus.
* Add validator for environment variables.
* Refresh canvas when user cancels edits so that the discarded sheet is
cleared from the schematic.
* Add file name validation to the sheet properties dialog to prevent
illegal file name characters from being entered into the text control.
* Rename FOOTPRINT_NAME_VALIDATOR to FILE_NAME_CHAR_VALIDATOR for clarity.
* Replace illegal file system characters when reading legacy libraries to
prevent FPID parsing errors and allow saving to PRETTY file format.
* Create validator to filter illegal file system characters from footprint
name text edit controls to prevent issues when saving to PRETTY file format.
* Add missing source file licenses and some minor coding policy fixes.
Wayne Stambaugh
jean-pierre charras