Separate the localScheme and hdfsScheme from FileSource.

This will enable the reuse of the *Scheme traits with a new subclass of SchemedSource that is not a FileSource.
Add a TemplateSource class.

This provides access to the cascading TemplateTaps through a scalding Source object. Follows the pattern of FileSource.
Adds tests for the new TemplateSource.
Cleanup documentation and imports.
Extract createLocalTap from FileSource.

Fixes compile errors in scalding-commons.
Merge pull request #726 from lewchuk/develop

Enable use of Cascading TemplateTaps in scalding.