Add arXiv data to database

[dasaderi]

No description provided.

[blahah]

This data was added to the db initially, and then removed because of issues with arXiv metadata. Specifically, some author names and titles contain LaTeX markup which needs parsing into the correct UTF-8 characters. I didn't yet find a good way to do this consistently.

[dasaderi]

Update after call with WinGravity:

This is something that we should do only if we want to fix the issue of the search. See issue #64. Currently the arXiv data is not all in because it's huge and Rik did not finish importing it (as far as I understand).

[blahah]

The issue with ArXiv was that there are LaTeX characters in the metadata and I didn't find a nice solution for rendering them well. I have just seen this potential solution: PREreview/getpreprints#6

[blahah]

If this was solved would you mind sharing the solution?