Creating an easier interface for hdf5 files

[Iximiel]

This should be the 0.1 feature:

• A way for the user to get and interact easier with trajectories out of the hdf5 files
• An instrument that reads the groups and makes some assumptions about their content, to show the user faster the content of the files
• I should not over-engineer this
• Maybe create a reader compatible with MDA

[Iximiel]

This may not be a necessary feature in the short term, the code now has methods to extract auxiliary information from the trajectories groups