Some files (notably in development/) had MPL-2.0 headers already.
The MPL-2.0 is the Apertis project's default license: it keeps
things simpler if we use it for anything that doesn't have other
copyright holders and isn't a contribution to existing software
under some other license.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Emanuele Aina <emanuele.aina@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D6855