Grimoire underwater rules

Feature Overview
This feature will allow for changes to spells when casting in an underwater environment. This feature has been tested and does work. The remainder of the alternate spell scripts still require coding.

Development Notes

 * spells.2da was updated to include column UndWaterScript. This is the script name to fire if underwater.  It takes 3(4) possible values.
 * 1) normal - fires the normal spell script
 * 2) no - this spell cannot be cast underwater
 * 3)  - a maximum 16-character name of the alternate script to fire.
 * 4) aaaaa (for testing only) - this placeholder script is currently used to denote which spells need to have an alternate script written for them.
 * sg_spellhook.2da was changed to do the following:
 * 1) Check if caster has had UNDERWATER variable set.
 * 2) if so, read the UndWaterScript value for the spell from spells.2da
 * 3) depending on value read, take appropriate action
 * values get set on caster to prevent infinite looping