[#252] Removed all xml:lang attributes except default from XML
[#252] Updated language tag check
[#252] Remove correct child nodes
[#252] Removed unnecessary child.getparent() call
[#252] Merge branch 'develop' into feature/252_multiple_lang_tags
[#252] Add check for akvo name space

A number of times when running the IATI XML import the namespace
definition for the akvo name space has been incorrect. This leads to
errors of course, but it is very hard to trace the origin of the
probelm.

Fix by adding the AKVO_NS setting and add an assertion at the start of
the upload to make sure the name space is correct.
[#252] Added AKVO_NS to __init__.py
Merge pull request #532 from akvo/feature/252_multiple_lang_tags

[#252] Import XML check for xml:lang attributes