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.