Remove Locking Logic from Server

[ngparas]

Locking logic is currently implemented in server.py. We should consider pushing this logic into the storage instead of the server itself. For example, suppose we used something like sqlite or redis to handle the package metadata instead of writing to the PACKAGES file directly. We would prefer those handle locking over doing it ourselves, and it would allow multiple instances of the server container to run concurrently.

This issue addresses the TODO left in the code here:
https://github.com/UptakeOpenSource/cran-server/blob/master/cran-server/server.py#L102

[ngparas]

This is related to #8

[ntdef]

Oh hey I fixed this in PR #25

[ntdef]

Resolved.