sw: merge SwXMLBlockListContext.cxx into SwXMLBlockImport.cxx

... so all the import is in one source file not 3 tiny ones.

Change-Id: I239316ec54cab28a7af643372af33782f70e7040
sw: clean up namespace prefixes in SwXMLBlockImport.cxx

Change-Id: I64716c9d087d1e9d3e76d14d555768af486e8982