[SMALL, RevEng] Map SQLServer xml columns to string properties.

[lajones]

Partial fix for #3076. Update RevEng SQL Server provider to map xml columns to string properties.

[natemcmaster]

Have we considered the limitations of xml data type? This simple PR works from database => model. Does EF handle xml columns types the other way?

[lajones]

@natemcmaster Yes - I did some testing and EF handles insert, update and delete going the other way. You can get into problems if you try to store some (but not all) non-XML e.g. ">'<" causes problems but just "someText>" does not. You get a DbUpdateException which explains (in the inner exception) that it had trouble parsing the string as XML. Discussed these limitations with @rowanmiller and decided they were OK.

[rowanmiller]

Yeah I've done some playing around with it for demos etc. and it works for the mainline cases just fine.

[natemcmaster]

Ok. Changes here look fine then.

[lajones]

Checked in with commit a8b185f.