Fix XPath problems

[ibboard]

The only XPath query that appears to return a value is "*". Currently the UnitType loading uses an XPath query for "stats" and Category loading uses an XPath query for "categories" but both return empty lists. This means that exceptions occur because required values are missing and WarFoundry XML files can't be loaded.

[ibboard]

(In r77) Fixes #45 - Fix XPath problems

• Include namespace prefix and namespace manager in SelectNode calls, as per remark at ​http://msdn.microsoft.com/en-us/library/hcebdtae.aspx
• Add SelectNodes method that always adds NamespaceManager
• Fix XPath queries

Also:

• Add Army XSD to settings schema cache
• Stop using deprecated Category constructor

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Mark fix as released under a previous version