adding uncertainties (part 3)

- updated 03_calculate_systematics.py, only missing ttbar theory systematics now
- added tuple (value, error_low, error_high) to Graph conversion
- added systematics calculation
bug fixes
adding ttbar theory systematic
replacing the final systematics JSON files with devations from central (was measurement)
remove calculation of uncertainties from plotting script
tidying things up
sorting the systematics for the plots normalised_xsection_*_altogether and splitting them up
fixing the calculation of the systematics
splitting plotting macro into ROOT and matplotlib
removing 'measured' from final plots and renaming 'unfolded' to data
commenting code back in
fixes for HT and ST, adding combined plotting
Merge pull request #23 from kreczko/master

Adding ttbar systematics + bugfixes