Implement #163 by adding token based auth
Token based auth can be switched on or off by setting the TOKEN_AUTH
environment variable, the value is not important, if the variable is set
then token based auth will take place.
The tokens used as a verification source are stored in S3, the S3 bucket
and key name can be configured with the TOKEN_BUCKET
and TOKEN_FILE
environment variables. The format of the file is the same as the files
userd for haproxy tokens.
As part of this I have also removed the feed api since it is no longer used. I have left most of the internal mechanics in place though, they are used as part of integration tests and unpicking that now is a reasonable amount of work.