refs #5856 & #6851 Experiment info converted into methadata

This commit goes for both tickets as we need to have run_number as methadata too.
refs #6852 Should solve the ticket

in theory. Test are still needed.
refs #6852 Unit tests for exporting W-matrix

Does not compile yet as matrix property is not implemented properly yet.
refs #6852 W_matrix is the workspace property and can be retrieved

tests show that.
refs #6852 A bit more tests
refs #6852 Stupid warning on Linux
refs #6852 Unit test which checks that EI saved and loaded from NeXus
Merge branch 'feature/6852_WMatrixAvailibleOnWorkspace' into develop
Merge branch 'develop' of https://github.com/mantidproject/mantid into develop