RequestInterceptorTest + some cleanup of existing tests

- Created RequestInterceptorTest to show a null request interceptor behavior when there are SSL errors.

- Created ServerWithInterceptorMain so I can place embedded mode in debug.

- Hooked up to Travis CI, including adding the status to the top of README.md.  Once merged, this will probably need to be updated to use a different Travis CI build aside from my own?  Or simply remove it.

- Cleanup of existing tests:
  * Extracted some common/duplicate variables into constants such as port numbers and URLs
  * Minor refactor to make use of existing @Before & @After methods with startup/shutdown logic, or added them.
  * In order to run in CI which doesn't have FireFox, adding Junit Assume logic to skip the FireFox tests if it throws a WebDriverException.

Regarding skipping FF tests: A follow on could probably be done for environments which do not have PhantomJS.  Thankfully, it seems Travis CI has that.  And speaking of CI, what do you think of Travis CI?  I just ran across it.  I am more familiar with Jenkins and TeamCity, but am not aware of any free hosted services.  If you know of any, I can look into hooking it up for you.

-Verna