Adds 1 new Searchlight option to MegaMek Client options.

[Sleet01]

1. Start with Searchlights on [Default: true] = Searchlights are set on at Deployment; this gives the benefit of higher visibility from the first activation.
   2. Searchlights toggle on/off [Default: true] = Searchlights, once turned on in the Movement phase, remain on until toggled off in the next movement phase. (This turned out to not be necessary)

Setting both options the first option to "On" (default) makes Searchlights automatically start on and stay on for night missions, which some users have requested.

NB: Because of the way Searchlights are implemented, toggling a Searchlight off does not effect that movement phase, but will persist from the next phase.

Tested against Princess in various night conditions; confirmed that Searchlights still work correctly and Princess still uses them correctly.

Close #4930

[kuronekochomusuke]

think you still need to entity.setIlluminated(false) each round while not isDeployment()

just always set to to false there and the setIlluminated will leave it on if you have the search light on

public void setIlluminated(boolean arg) {
    illuminated = searchlightIsActive || arg;
}