Initial commit of open-source Thor project

Summary:
Initial commit of open-source Thor project. This includes a bunch of base-classes that RdioThor inherits from and overrides. This _excludes_ statsd, slf4j logging package (defaults to Twitter logger), arbitrary helpers and is just a barebones image service built on top of scrimage+finagle.

Work to do:
- We need a maven repo (even a public one we can publish to). I don't know what's involved there. Right now I'm "publishing" to a local ivy repo (see build.sbt) and importing the classes into my local RdioThor repo as I would any other library, which is nice and clean.

Test Plan: Manual. Tests pass. Scala-style mostly passes (it could be better, will look into improving it). It compiles and runs locally, serving images if media host is available.

Reviewers: joseph.norton, jesse, justin, msmith, rebecca.stecker

Reviewed By: joseph.norton

Differential Revision: https://phabricator.rdio.com/D11601