Add TLS stack investigation concept design

Future changes to the licensing of some TLS implementations are
compounding an already uncertain licensing situation. Add a document
describing the situation; an analysis of options to rectify this and
our recommendations.

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
Signed-off-by: Martyn Welch <martyn.welch@collabora.com>