Added a more useful logging function

Added "/Core/Server/ActivityLog.pwn" script that simply logs a string to
a dated file (different file for each day) currently being used to log
explosive use. Useful for finding hackers who get into bases without
using explosives.

Added a "/deletesigns" admin command and improved the DestroySign
function for use in loops.

Added TimestampToTime and TimestampToDate functions.