Adding validation for bdew load profile sources.

[staudtMarius]

Resolves #1243

[danielfeismann]

Thanks for including some validation. Some minor suggestions from my side, take into account what makes sense to you.

I would be happy if we could add some test for the dynamisiation function of the H0 profile.

[danielfeismann]

Thanks for including my points. Just two minor last things :)

[danielfeismann]

Looks good to me, thanks for taking into account adding some validation!