Various bug fixes for the Go to Line feature

Fixed grammar ("Goto Line" -> "Go to Line...")
Corrected the minimum and current line number in go to dialogues (off by
one)
Made "Go to Line..." for the dialogue editor select the line to match
the script editor's behaviour
Removed the thousands separator from the "Go to Line..." number spinner
The number in "Go to Line..." is now selected whenever it receives the
focus
Reimplemented SelectCurrentLine() so it now works correctly with double
char line endings (chr(13)+chr(10)) and selecting the last line of the
file
This addresses concerns outlined in:
http://www.adventuregamestudio.co.uk/forums/index.php?issue=436.0