1.51 update

Update 1.51 contains:

- added bot support (acessible via the options menu).

- 2 new maps: Bogota and Alma.

- 2 new grenade types: C4 and a deployable turret.

- 2 new secondary types: infravision googles and the bear trap.

- broader options in the options menu.

- level select and loadout select screen now usable with controller.

- reworked the zombies mode, so that it now works on rounds.

- added ladders, reworked alot of maps.

- grenade indicator and reworked grenades to be more effective.

- frontier shotgun was replaced with the double-barrel shotgun (due  to balancing reasons).

- C4 belt perk was integrated into the martyrdom perk.

- minor tweaks to balancing and game feel.