Improve date storage

[slingerbv]

Currently, we're not storing the date of a method's last change. We want to have better dating for each method.

[slingerbv]

@ra5put1n please elaborate

[ra5put1n]

Currently, the miner stores the date of method as the date of the last edit for the file. This is not accurate as the method could be added much before the last file edit.

To solve this, we can either recursively check the file changes in every commit for every file during the parsing process. That would be resource intensive and will increase the take the time taken for parsing a repository (impact needs experimental verification).

A better approach would be to have a service which does the date computation when a check request is recieved. That is, whenever a project is queried, all the matched functions' dates are fetched through the file commit history. This way, we only perform computation for matched functions while also not consuming time while mining.