Editor improvements (see description)

-Editor now uses a monospace font
-Tab width is now 4 (will be configurable later, but 4 is a good
default)
-Starting position of cursor is now nicer (no longer puts the error line
at the top of the window when opening the file)
-Double-clicking an error in a file that already has a window open will
now focus that window and scroll to the correct line, rather than
opening the file a second time
-Line numbers now scroll when the file's text is scrolled
-Defaulted word-wrap to off for now.
-Fixed infinite loop when opening a file with a multi-line comment in it