* 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.
jean-pierre charras
Wayne Stambaugh