Unzip datafiles feature

[AndrewWood94]

Adds ability to unzip datafiles and save contents as new datafiles, which can be linked to any assay the zipped folder is linked to.

Notes:

• A way to link multiple datafiles to an assay simultaneously would be useful if users forget to link in the unzip process
• Nothing is implemented to handle new datafile versions not matching the original zip contents, this could be added in a similar manner to updating extracted samples
• Unzipped datafiles do not have a creator, similar to extracted samples
• Currently no tests have been written for this feature

[stuzart]

code is good, and gave it a run through and test and it works quite nicely. thanks.

I will merge this and add some tests on a separate branch (since I can't push to this one).

If you agree, I also thought I could make the creators default to the same as the original zip file. I was also thinking of showing the origin zip file as part of the metadata on the data file show page.