user notification of new sorcery releases (Feature #309)

I'll just quote Ladislav from another bug:

I suggest a new sorcery feature:

"sorcery update" could note time of this update and sorcery commands (cast,
dispel, ...) always check that time and if sorcery is older than for example 14
days user is warning or even forbidden to run sorcery commnands (without the
option --i-am-aware-that-my-system-can-be-destroyed). Only sorcery update
should be enabled.

BTW, if users want stable system they shoud update their system at least once a
month, for example after stable grimoire is released. "sorcery update" is a
part of recommended "sorcery system-update".

We could check the version triplet and have different messages if it is just a patchlevel bump or a minor bump (new sorcery branch).

It could also be done in a spell, let's say basesystem (since it is a profile).