Fake units

This introduces `physicalSizeX` etc in the `FakeReader`. String endings can be used to modify what unit is used. e.g.:

 * `...&physicalSizeX=1.fake` uses the default
 * `...&physicalSizeX=2ft.fake` uses feet, etc.

A couple of other fixes are added here that were necessary to get imports working correctly:

 * A build fix which broke with the introduction of version.xml
 * The return value of the `unit()` method.