source: show file being edited in window title bar

Dependencies

• [2] OMLASW7K experiment at avoiding some merge conflicts
• [3] CEDTFKFD delete some dead code
• [4] X3CQLBTR set window title within each app
• [5] KKMFQDR4 editing source code from within the app
• [6] YMNOUE2M ugh, missed deleting an arg
• [*] ZTK4QTZT extract a couple of functions

Change contents

• replacement in source.lua at line 77
  [2.104]→[4.11:57](∅→∅),[4.167316]→[4.11:57](∅→∅)
  − love.window.setTitle('lines.love - source')
  [2.104]

  [2.105]
  + love.window.setTitle('lines.love - source - '..Editor_state.filename)
• edit in commands.lua at line 133
  [3.68]

  [8.164]
  + love.window.setTitle('lines.love - source - '..Editor_state.filename)