Convert Crab Bombs into a Global Script

[Causeless]

Describe the Problem and Suggested Improvement
Crab bombing was an effect caused by old technical limitations to the game that were removed a long, long time ago. Effectively, the combination of crabs being free with very restrictive MOID limit meant that spamming crabs would quickly blow this limit, causing all non-brain actors to gib.

In CCCP build, this was readded to the code as an explicit 'feature' for nostalgia purposes, but it's such a specific detail that it ought to be removed from the C++ entirely and done via script.

Describe Additional Work Required Before Improvement Can be Made
The old crab bomb settings will need to be removed from SettingsMan, and have the vestigial crab bomb C++ hacks removed. Afterwards, a global script can be created that, when enabled, will re-introduce the crab bomb behaviour.

Note that global scripts, as of yet, lack the ability to have user-variable settings, e.g the crab bomb threshold. I suggest that the theshold is just set to its default value of 42 in the script.

Additional context
The commit that added the crab bombs was ce87d40.