Reagent Bag

* Reagent Bags now exist. A player can have only one. The reagent bag
cannot be dropped. Any reagents acquired will automatically go into the
bag. Right clicking on the bag will show the contents, and a stack of
reagents can be pulled out for sale or conveyance. Reagents in the bag
will be found and burned by spellcasting. This should significantly
clean up our inventory space.

- The bag does not change your carrying capacity. Any reagents in the
bag count toward your weight hold total. However, if you are full, you
can still always transfer between your bag and your own inventory.
There are no annoying capacity issues. The reagent bag itself weighs
nothing.

- For the time being, reagents in the bag don't drop on pens or death.
The exact mechanics there need to be discussed by the team.

* Reagents have a new application property. Double-click a reagent and
use it on a reagent bag to stash that reagent in your bag. Spacebar also
activates this ability, as well as the 'u' key when the reagent is highlighted.

* Upgraded Holder class GetBulkHold and GetWeightHold to calculate their
bulk and weight whenever they are asked, rather than keeping track of a
property. Deleted the property, so all holder objects will lose
piBulk_hold and piWeight_hold and cause a thousand errors the first time
this update is used.


"You stash 100 emeralds in your reagent bag."
"You get 100 emeralds from your reagent bag."