New fishing content

EDITED AS OF 24/9/14:
1)Some more fishes (and some z-fishes) were created and they are added to the RIVER_GROUP spawnlist, as well as the FISH_GROUP list.
As such, they spawn normally. ( i expect the spawn chances to need lots of tweaking)
2)Z-fish added are: Zharks, Mutant Carps, Mutant Salmons
3)Fish with traps catches one of the existing fish around it.
4)Trap fishing now lasts 3 hrs.
5) Fished corpses rot according to when they where fished (do not start up as fresh)
6) Fish-with-rod action catches fish from the spawned.
7) The pro fishing rod has been added, as well as its support code and spawnlists.
8) Reviewed fish stats
9) One function handles the monster catching for all fish activities, and can be used for general monster catching (when the catched dies as well)
10) The "the xxx dies" message was stopped when catching a monster. (eg. when fishing)
11) Update the fishables vector every 30' when fishing with traps, instead of getting just one vector regardless of fishing time.

TODO: [Maybe in another PR] Find ways to adjust the fish population (and the fish spawns accordingly) in response to fishing and time passed from the start of the cataclysm.
You can't store pointers to monsters from the Creature_tracker. Those pointers don't stay valid over time. Look at the implementation of Creature_tracker (`game::zombie(int)`, `game::mon_at(...)`, etc. refer to this class).

When a monster dies, it is (at the end of the turn) removed from the vector in Creature_tracker and the monster object is deleted, the pointer to that monster (which you have stored) is now invalid. Also `items::catchables` is not stored when saving the game.