Support Unicode BOM in localization files

Remove the BOM, if detected, before processing .l10n files.

Also change a comment in quearl_inst.py, since the changes in commit
6ab6260bb24b739523d8d5a1b40d80f16a8762a2 really work for any UTF encoding,
not just UTF-8.
Make script output more structured

Add an indentation on several lines output by off-line processing scripts.