SlimerJS support

[bentrm]

Work in progress. This addresses #286 and I would like to discuss how to continue.

The run-testsuite.js has been altered to use the http:// protocol of a static file server (Python SimpleHTTPServer, Node.js http.server) which makes it compatible with SlimerJS. The .travis.yml has been altered to run the test suite via engine PhantomJS and SlimerJS. This leads to two problems:

• Some tests fail with SlimerJS, I haven't checked yet if this is a problem in the code base or in SlimerJS support.
• SlimerJS does not return the correct exit code on error. This is a known bug.

[marcjansen]

Great that there is some progress here. I fear I will not have time to look into this for at least another week. I fully support any work towards more browser engines.

[marcjansen]

WRT to slimerjs returning 0 all the time, we could capture the output and grep it afterwards for

FAIL 775 tests executed in 57.494s, 774 passed, 1 failed, 0 dubious, 21 skipped.

[bentrm]

We're greping the error code now to reflect the build success in travis-ci results.
The idea for run-slimerjs.sh is from this site.

One test for panel/Map.html is failing in Gecko:

799) Caught exception:  [calling method, test_getState(t), panel/Map.htmlTypeError: state is undefined]

Running the test locally there would be an occasional hiccup/hang up with an error described here. I haven't been able to find the reason for this nor did I find a way to reproduce this steadily.

[bentrm]

@marcjansen I think we can drop this?

[marcjansen]

I need to postpone this for some time. Anyone else?

[marcjansen]

Let's wait some time before we close it. I may have some time for this... not sure though.