Cope with non-cm image dimensions

Style-related operations are slowly being moved towards px as the
default unit to improve consistency. Standardising getContentSize to
work in px rather than cm provides better re-use of CSSUnits as well.
Ignore test-generated ODTs
Provide better fallback mechanisms for Formatting.getContentSize

getContentSize will now always return a valid page size, falling back
to it's own hardcoded format if no valid one is found for the document