Improve line wrapping handling

This fix https://github.com/traff/jediterm/issues/24 :

- `TerminalLine` is aware of wrapping state, making multi-lines copy/paste working properly.
- Fix bug when resizing, filling current line with unwanted spaces.
- Fix bug when resizing, where the end of current line is not cleared properly in text buffer.
- Triple-click line selection is aware of line wrapping