Dependency activity collection

[andrew]

First attempt at collecting and storing dependency activity in the database for https://github.com/librariesio/libraries.io/issues/1603 and ultimately https://github.com/librariesio/supporters/issues/21

Adds a method to clone a repository, analyse its history (using repo_miner) and then store each action as a DependencyActivity record, including finding the project id by it's name in a process (if possible)

Includes a few indexes on the table but not 100% sure what we're going to want to do with the data yet so keeping them to a minimum for now.

~~Partially blocked by https://github.com/librariesio/repo_miner/issues/2 right now~~

[andrew]

@BenJam gunna hold off on merging this until the open data release prep is done, mostly because this will put an unknown amount of load on the queue 🙈

[BenJam]

👍