First pass at generating cobertura-style output using string templates

These changes are by no means complete, but I wanted to get some feedback on them before continuing development.  I know the ultimate goal for Saga is to get away from string templates for reports, however, I think using string templates to generate the cobertura report for now is much simpler.

One key bit of work that still remains is to group the files by package/directory so the results are easier to look at.  Currently, all files will end up in a default package.

One other change I had to make but didn't like was adding a "sourceDirs" property to the configuration in for the maven integration.  I couldn't find any other good way to populate the source directories in the cobertura report, especially when Saga was running with Jasmine, where all sources appear to come from http://localhost:1234

I would also like to be able to generate complexity statistics, method coverage, and branch coverage in the future, but that's going to rely on other work to get those stats from the coverage generators.

If this seems like a good start, I can continue the work to group the coverage by package/directory.