Comment 30 for bug 168164

Patch with these improvements:

* Fixed arrow tooltip
* Points is the default font unit. Do we also assume svg like "font-size;10" is also 10pt ? Currently it is assumed 10px.
* Changed the default drop-down list of font sizes to be relative to the preferred unit
* Added em unit preference.

Some observations related to "em" :
1. Inkscape uses 12px as the "default" font size. So if you have a file with "1em" font size, it is rendered as a 12px font.
2. Chrome and Firefox seem to use 12pt (16px) as the "default" font size.
3. The "Set as default" (in Text dialog) does not change the above 12px default. This means users cannot create a "relative" layout using "em" sizes, then resize it by setting the "default font size"
4. "Set as default" is currently disabled for "em" unit - due to bug #1036010