Increase test coverage. Add performance tests, and refactor the implementation a little.

but users might use it too. Wanted to make a separate ticket for this but trac is down

Refs #3724: Pulled wiki description text from the wiki site and added in algorithms' header file with special tags. The auto_wiki.py script can retrieve the text to generate the wiki page fully.

Refs #3507. Full-move to MVP. Sorry for large checkin, but these things are all dependent and cannot have partially working GUI code.

Refs #3157 Sort our System.h. It was becoming a dumping ground. It should only be touched when absolutely necessary as it affects every file in Mantid. Also combined this with Refs #2345 to sort out DLLExport/DLLImport usage. It's done for Kernel, Geometry and API but stuff in the plugins could do with updating as well.

Do away with MantidPlotReleaseDate.h and have everything in MantidVersion. Turn MantidVersion into a class with static functions so that the part that changes every time can go in a cpp - this means files that include MantidVersion.h (e.g. the enormous ApplicationWindow.cpp) don't get compiled every commit. Re #2722. Also formats date better, which fixes #2246.