Simplify time options

These 3 `Emergency` options are not suitable fo end-users. Nobody
understands what they do, apart from those who delved into the code.

For end-users, only one option should be required to adjust for lag. This
is also more consistent with what other engines do.

As for Move Horizon, I see no reason to change its value. Seems better to
hardcode it as 40, and tune the Emergency Move/Base Time instead.

At the `timeman.cpp` level, the full flexibility is kept as it was. The idea is to
not expose the complexity to the end user, while retaining the flexibility for
programmers.

No functional change.