Remove duplicate enums

Create Core library and copy all enums in as to remove duplicates
Potentially some other code can come out into Core lib as it's used by
both PdfSharp and MigraDoc
Fix TestFormsApplication

Add image so testformsapplication works as expected
Cleanup Unit class as well, potential to make a few improvements to this
class in the future (as it's used a lot and converting from a string to
Unit is relatively expensive)
Update Hybrid Project

Update the hybrid project with core changes
Use resharper to cleanup code
Optimise usings
Resharper Reformat Code

Full resharper reformat over entire PdfSharp project
Remove NET_Zip code (was no longer used)
Fix minor error in XGraphics

Minor error introduced as part of cleanup