Add dateparse and DefaultTimeFormat

[Houtmann]

I dot this pull request because in reality when you write an OCPP central system server, you may have more than one brand of chargepoint on the same central system.
For example in my company, we have 4 brands of chargepoint connect on the server.
And in fact chargepoint's brands do not meet the standards DateTime.

The library dateparse allows us to deal with this problem;

[lorenzodonini]

Hey Had,
you make a good point there.

I originally thought of keeping the included batteries to a minimum and enforce the specifications, which clearly say that:

• ISO 8601 MUST be used for OCPP 1.6
• RFC 3339 SHALL be used for OCPP 2.0.x (except for meter-aligned data, which still follows ISO 8601)

Imho charge point vendors should conform to these standards, however it makes sense to provide some flexibility for devs.

It would be really nice, if you could add the same change for the ocpp2.0/types package directly (the code is basically the same).

[Houtmann]

All right, I'll do that. As I said, 4 different brands, 4 different date formats...

[lorenzodonini]

Just checked out your branch and ran the unit tests.
Some of them are now failing, apparently because the datetime equality checks are not passing.

Can you make look into it and figure out why? Otherwise I'll do it as soon as I have some time.

[Houtmann]

Yes I'll look into the problem