Allow requirement vectors to check visible boolean server settings
A ruleset may wish to adapt to server settings like unreachableprotects, restrictinfra, killstack etc.
Limit to visible server settings. It is a good idea to only give access to "rule" server settings. (Exclude "internal" and "network" settings except victories)
A boolean server setting is enabled or disabled. It is therefore enough to specify its name in the requirement syntax. It could be expanded to a syntax like "settingname=valuename" if support for other server setting kinds should be wanted in the future. (enum, bitwise and (lov range) int server settings could be multiplexed with the server setting id)