- reworked dimension settings
- for pixmaps the remembered setting is zoom and the user can alternatively
  control width or height of the image in pixels
- for vectors the remembered setting is physical pixel size and the user can
  alternatively control width & height of the image in mm or pixels per inch


git-svn-id: svn://svn.code.sf.net/p/gwyddion/code/trunk/gwyddion@16657 25697fe4-d644-49b8-9d30-be5465f2adf3