LOK DocView: clean up document on exit.

Otherwise lock files etc. aren't cleaned up, which isn't particularly
nice should when then opening the file in normal LibreOffice.

Change-Id: I822b6fb582473674371a4c1d403d5a05adb7ea6b
Turns out document coordinates are already in TWIPs.

This now means that fonts are also correctly scaled,
whereas the 100th mm mapping caused fonts to be scaled
differently to the grid (i.e. looked ugly).

Change-Id: Ib8b913490823a7ba406e52291e52d50053ae32b8