Use environment variables for Facebook secrets

[nateeo]

Addresses the secret keys issue for #22

@st970703 @crat019 I propose simply replacing the getter for the keys with a System.getenv call. This would mean providing secrets as environment variables on the application host. If you think this is fine, I can also remove the old environment code.

Also we should probably add an option for setting these variables in the bash script as mentioned by @TheGuardianWolf

[nateeo]

@jsoulsby @Jcen902 ready for review

[Jcen902]

Good idea. Good to go

[nateeo]

@softeng-701 ready to merge

[softeng-701]

@Nateeo Please resolve the conflicts!

[nateeo]

@softeng-701 done!