Switch from errbit to getsentry
[BIS2027] add subject filter for teachers

[podio story](https://podio.com/bitzesty/bis-phase-2/apps/stories/items/29)
Use ENV Variable for getsentry
add travis config file
Merge pull request #26 from bitzesty/BIS2027

[BIS2027] add subject filter for teachers
Do not fatal if `ENV['GETSENTRY']` isn't set
add travis badge

So that we don't break it
Merge pull request #27 from bitzesty/optional-sentry

Do not fatal if `ENV['GETSENTRY']` isn't set
Update Rails
Merge pull request #29 from bitzesty/4.0.5

Update Rails
update gems
[BIS2029] use passenger
update gems
Merge pull request #28 from bitzesty/BIS2029

[BIS2029] use passenger
switch to passenger
setup caching