py3: Add six to dependencies
py3: Fix html-related imports on Python 3
cleanup: Replace dictutils.ordereddict by collections.OrderedDict
accesskeys: add properties to bad accesskey detector

Extended the script to check for bad accesskeys in .properties files
six: this is now a hard dependency

Previously our dependencies where all optional, but now we require six
to actually run the toolset.

Add requirements parser from Pootle.
roundtrip: ignore the noise created by roundtrip scripts
Generalize entity encoding/decoding code

So that it can be used with custom set of entities.
Handle nonentities at end of string

We were passing through things like ”&copy ” (notice the space) but not
“&copy” (no space) which was completely dropped from output.
Don’t touch existing entities in entityencode()
Use quote.entityencode()/entitydecode()

They provide more sophisticated handling of entities than blind replace,
will allow us to handle the ampersand properly.
Support &amp;

The roundtrip test for “&amp;nbsp;” is failing, need to find out how to
fix it or whether it is a valid input or not.