Defer mode flags for AddRemoveReaScript()

So that a defer script can be installed with the flags alerady set and the user doesn't have to deal with ReaScript task control dialogue when the script is terminated for the first time.

Not quite. This function doesn't change the flags in the reaper-kb.ini file, it only affects script behavior at runtime.

I'm all in for that one! Would help tons with ReaPack-installed-scripts.