Comment 2 for bug 1422926

Tying the GUI units for font size to 'Display Units' won't work well (as discussed with gez on irc), here's a better proposal:

1) A global preference sets the default value for the font size units (already exists)
2) NEW: A unit selector is added to the text tool controls bar for the font size
   (allows to override a global or per-document setting temporarily in the current session)
3) NEW: In Document Properties, a new setting is added below 'Display Units':
'Display Units for Font Size', with values [ Default | px | pt | pc | mm | cm | in | em ]
'Default' would use whatever is set in the global preferences, any other value would be stored in and retrieved from the current document.
4) NEW: Templates distributed with Inkscape:
- print-oriented templates (know page formats, display units like 'mm' or 'in') use 'pt' for font size units.
- webdesign-oriented templates (defined in 'px' dimensions) use 'px' for font size units.
- if display units for font size size is undefined, the value from the global prefs is used.