datetime for repost_time

[thekingofcity]

Use system's cert instead of disable InsecureRequestWarning

https://urllib3.readthedocs.io/en/latest/advanced-usage.html#ssl-warnings
https://urllib3.readthedocs.io/en/latest/user-guide.html#ssl

https://stackoverflow.com/questions/42982143/python-requests-how-to-use-system-ca-certificates-debian-ubuntu
https://stackoverflow.com/a/33717517/1695680

In this PR, we use system's cert rather than third-party certs. However, this will downgrade the compatibility since only ubuntu(debian) use this path.

[thekingofcity]

In 4d80e0b, the create time for repost was updated to use datetime(python) and Datetime(mysql). This is a BREAKING change for the current project and means no more compactability for the previous database schema. However, by extracting the common create time parser, the repost and comment tasks can be maintained at once. And also the reposts can be filtered by create time via where. So this should be a helpful update.

Since the last PR heard no comments till today, I may merge this in the coming few weeks if there is still no any comments.