- Prefer "png" over "svg" because for Tango theme we include both
  "png" and "svg" icon, but rendering of "svg" crashes
- We save the choice of which icons to use into the profile. When
  32px icons were added the values have shifted - "auto" had value
  2 has became "32px" choice and "auto" has the new value 3. In the
  case of the default "auto", we now always showed 32px icons. This
  commit reverts the "auto" value 2 and puts "32px" choice to 3.
- Name resolving now always removes the icon file extension and
  adds the ".png" and ".svg" extension before resolving. This
  makes it possible to define the name of the icon without the
  file extension.

Change-Id: I05e3913aaee0037692609ced246954b14a13828a
Reviewed-on: https://gerrit.libreoffice.org/30440Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Tested-by: Tomaž Vajngerl <quikee@gmail.com>