Fix conversion of successive Gaia plural units

When a plural unit is followed by another one, we were failing to output
the first one. Another repeated code block, but that is for the next
commit.
Refactor code repetitions
Add Gaia roundtrip script

Based on roundtrip-mozilla one.
dtd: Use source accesskey if target accesskey is missing
dtd: don't remove stray & as they probably &amp;

Since we now convert & -> &amp; we no longer need to worry about these busted
ampersands.
accesskeys: don't use space as an accesskey
PEP8: E101 indentation contains mixed spaces and tabs
typo
Docs: Add example on using --columnorder for csv2po
docs: Add deprecation guide
buildxpi: restore `--disable-compile-environment`

Mozbug 862770 has already been fixed.
properties: handle \uNN

Slight change in processing to make sure that we don't bitshift if the
char is not a hex char.  The code worked otherwise.

Note: Java does not support \uNN or \uNNN.  But it can't hurt to support
this in either.
properties: escape leading and trailing spaces

Otherwise Mozilla’s parser will “eat” them.
docs: update Wikipedia as part of release process
Docs: Fix typo in releasing instructions
Docs: Remove not applicable link in TTK release notes
Docs: Add notice in changelog to refer to release notes for latest releases
Docs: Moved changelog for 1.11 to the release notes
Docs: Moved changelog for 1.10 to the release notes
Support for new Subversion client storing data in one .svn directory at top level