Set Build Action to None for dictionary XML files

As noted by @divieira, the Windows Store DLL would not be correctly
included in external applications, but a "payload file missing" error
message would instead show up. Since only the xml.gz dictionary files
are used by the class library (and the .xml files merely included for
reference) I have changed build action to None for the .xml files to
prevent these files from being referenced in the DLL.