Add new behaviors to level

[fatjosephina]

Get checkpoint system in level, get train in level, get working barriers in level, get more pickups in level, continue refinijng enemy interactions, start second half of level

[fatjosephina]

• [x] Checkpoints throughout level
• [x] Beehive interaction implemented with timelines and particle effects
• [x] More pickups in and around Research Lab Alpha
• [ ] Smoke coming from distance from chimney and possibly craters
• [x] Elevator enemy interaction implemented, gun unblocked after killing enemies
• [ ] Secret area in Research Lab Alpha
• [x] Boost pads
• [x] Key and door working
• [ ] Some more art around the train station
• [ ] Elevator doors

It's possible that not all of these will be able to be implemented before Release 4.