Adds new Save As action to Scripter File menu with Ctrl-Shift-S binding.

Some consequential changes:
Existing document.Document class write file using print. This adds the default carriage return character at the end of the print/file. Changed to file.write()
File validation in Save action was redundant as it's already handled by QFileDialog. I could not trigger an exception when using the file dialog. It also didn't specify an exception type. Bare except clauses are frowned on. Have removed try: except: structure.
Removed unused imports
Added docstring and new save_as parameter to DocumentController.saveDocument() method.

my ref: bbd/saveas

Open scripter

1. test changes to existing Save function

create new file
Save file - confirm saved
Save file with filename collision - test that QFileDialog displays an overwrite warning dialog

2. test Save As function

use existing file
Save As to new name - confirm saved
Save As with filename collision - test that QFileDialog displays an overwrite warning dialog