Standardize table time fields

[downdawn]

1、Each table, except for intermediate tables, should have create_time and update_time fields.

2、create_user and update_user fields are optional.

3、User table:
time_joined -> join_time
last_login -> last_login_time
user_uuid -> uuid
create_time
update_time

4、func.now() defaults to UTC time, but it should actually be the server time or Shanghai timezone.

[wu-clan]

Positive content, I think we should make some fixed trade-offs

create_user and update_user

1. in BaseMixin, but all are optional fields
2. Make them as separate Mixin, create_user mandatory, update_user optional

create_time and update_time
Provided as BaseMixin, required

user table
Agree to change them, those naming are unsurprisingly django's default

datetime
A separate time tool should be created with support for time zone settings, and global use of time zone time is a headache

[downdawn]

Yes. The second option might be better.

[wu-clan]

#152