Add exceptions initializer from starter repository

[gazayas]

Joint PR

• Remove exceptions initializer bullet_train#1043

[jagthedrummer]

@gazayas is there a reason that these need to be in an initializer instead of each error living in it's own class somewhere? I'm thinking maybe bullet_train/app/errors? Or perhaps somewhere in bullet_train/lib?

[gazayas]

@jagthedrummer No reason besides it was originally there in the first place, and I wasn't the one who originally made the file. I like the file being in bullet_train/lib, so I moved it over.

By the way the tests are failing in the starter repository because I accidentally named the branches differently...

[gazayas]

Will look into the failure that's coming up here, might be legit. Seems like the RemovingLastTeamException is not getting picked up.

[gazayas]

This one should be good to go. The tests are failing locally, but pass with the fix in bullet-train-co/bullet_train#1044