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.