indicate disabled crispness menu items
add reference regarding the origin of the color space translation routines
Revert "Revert "revert network packet size change""

This reverts commit 6fd1368540a4f7097eac1fcb2bd1b82148bdd7b1.
some features are also disabled in demo playback
fix features not re-enabled after starting new game
major Crispness menu overhaul
Crispness menu overhaul
do not fix common mapping errors anymore

After all, they are errors and should be fixed during mapping and not
by the engine. Also, fixing them is a rather drastic deviation from
Vanilla behaviour.

But, more importantly, some mapping errors are demo-critical. However,
due to the order in which variables are set in p_setup.c, it is
impossible to conditionally enable them with one of the "usual
suspects" variables, e.g. demorecording, demoplayback, usergame.
Instead, I had to introduce a new global variable that was once set,
but never reset. So, one ended up with two differently set-up levels
depending on whether the demo loop has been entered from the start
screen or not. Instead of fixing this in each possible location in the
code, I decided to remove the fixes entirely.