Inserting a completion no longer deletes text.

Updated the insertSelectedCompletion method with a workaround to fix this issue. Before calling setDisplayAutocompletions:NO withAnimation:NO, set insertCompletion to NO so that the deleteCompletion method (called when hiding the autocomplete view) does not delete any text.
Text spacing in the autocomplete table view now matches that of the text view.

This spacing issue arises from the use of screen fonts in the table view but not in the text view. Added a NSTextFieldCell subclass (PLAutocompleteTextFieldCell) that overrides the drawInteriorWithFrame:inView: method. In this method, draw the cell attributed string using the NSStringDrawingDisableScreenFontSubstitution option.
The use of screen fonts is now checked before displaying table view cells.

PLAutocompleteTextFieldCell now has a usesScreenFonts property. If NO, it uses the NSStringDrawingDisableScreenFontSubstitution option in the drawInteriorWithFrame:inView: method. PLAutocompleteViewController sets this property in the tableView:willDisplayCell:forTableColumn:row: delegate method.
Minor cleanup in setRowHeight method.
Hiding the autocomplete view now stops the completion timer.
Fixed behavior when inserting a space into the autocompleteTextView.

In textDidChange:, if the partial word range at the current location has a zero length (i.e. only a space character), hide the autocomplete view.
Cleaned up many functions in PLAutocompleteViewController and removed commented out code in PLTableView.