Revert "Correctly insert at an existing parent if appropriate"

This reverts commit bb04ce073bfd5e1543285074b20fedf54d3f6feb.

Tests are failing because of this change. Nothing seems wrong with the
change but it needs a fix to the related tests before it lands again.
docs: add ref for intersphinx links
roundtrip: run silently when roundtripping
dtd: underscore is valid in entity names

We where failing is_valid_accesskey when entity name contained _ which
would remove a leading & and make the entity invalid.
dtd: optional expected makes cleaner roundtrip setups
accesskeys: test numeric keys
accesskeys: test combining non-ASCII keys

The function actually claimed to return Unicode but was converting to a
basestring.  So this also drops that conversion to basestring.
misc: Drop diff_match_patch

Since it is not used anywhere within TTK itself, the requirement can be
dropped entirely
req: eliminate min-required.txt
req: sort requirements lists
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
Add LibreOffice checker

LibreOffice is diverging from OpenOffice so needs its own checker, right
now the checker is identical to the OpenOffice one, but changes will
follow.
Add new xml test and test for this test

Test translated strings belong to LibreOffice's
(and OpenOffice) help and readme, wheather xml/html
tags has their own open/close tag. This is the most
common build breaker problem with them.
Plus add test_validxml for testing
Adapt the previous commit to LibreOffice checker

And fix the coding style a bit.
setup.py: Simplify a version check now that we no longer support 2.5