make it possible to change local templates

The codegen of the thrift idl templates had used the templates that were
built into that jar, but then compiled those outputs against the local
scala sources. That made it really hard to update ssp's. So:

1. Bump to codegen plugin 1.4.2.
2. Point at absolute path of local ssp's.
3. Mark common-thrift-{base,json} as intransitive because the last
   release mistakenly published them with deps onto scala-2.10 which made
   everything sad.
Merge pull request #7 from nsanch/use-local-templates-for-thrift-bootstrap

make it possible to change local templates