Features/split tests

* First set of changes allows compilation on Mac + native Xcode compiler
* Second set of changes separates tests into more than on executable
* The tests now run via [ctest](http://www.cmake.org/cmake/help/v2.8.8/ctest.html)

The reason we did this is that some tests produce a large amount of reporting (namely, those in space), eg several hundred megabytes of it. This makes it difficult for jenkins to parse the results. At present the "space" tests' reporting are limited to unsuccessful unit tests, whereas other tests report everything. 

The result should be viewable on [jenkins](http://ulam.rc.ucl.ac.uk/jenkins/view/BEMPP/). They are run on a Mac and on a Red hat, using the UCL/bempp fork for now.  

Some tests fail. Please do check that it is not a compilation/environment error!

Another branch creates one test per file, rather than one per directory. We could go that route if preferred.