More informative error message in vtkweb-launcher.py

(Via zack.galbreath@kitware.com)
Merge branch 'informative-import-error'
Restructured CMakeLists to handle new testing infrastructure
Added Javascript unit testing infrastructure.

Jasmine is used to specify the unit tests, and PhantomJS runs the tests.  CMake
generates test suites by embedding various .js files found in
testing/js-unit-tests, into an HTML scaffold that includes code to take the test
results and report them nicely in HTML.  These files are placed in Tangelo's
default web space, and CTest generates invocations of PhantomJS to "run" the
tests using a modified run-jasmine.js.

Eventually, each test will need to depend on a test that launches the Tangelo
server.  There will be a similar teardown "teardown" test that will depend on
all of the other tests.  This will work somewhat differently on Windows, since
there isn't an option to launch Tangelo as a daemon there.
Added "web content testing" infrastructure, along with several content tests.

Removed some of the "old style" content tests (when they were able to be
replaced by new style ones).

Dumped "resolve" test.

Updated two of the test services to better format their results (better use of
spaces and newlines).
Added status code detection to content test runner.

Added a 404 test.
Added a "200 OK" test to replace the shell script driven test
Changed suite() to accept a config object; added "image file" option

Updated all content tests to new function signature.
Replaced geodots image comparison test with PhantomJS version

Removed "tangelo-server-test" infrastructure (no longer needed by any test).

Added promises mechanism to web-content-test scaffold (to handle asynchronous
processing).  I would have liked to simply have done certain things (like
waiting for image data to load) synchronously, but I've tried several tricks and
I can't force PhantomJS to work with any of them.
Restricting each test case to a single test.

Brought web-content scaffold up to JSLint code.
Added serverside (python) unit testing framework.
Merge branch 'testing'

Closes #190