[FeatureRequest] Add logging Frequency during training

[ORippler]

Description
Provide means to specify logging Frequency during training. For Visdom, all logging results are kept in memory (risking OOM), and with tensorboardlogger, disk I/O may bottleneck training otherwise.

Proposal
There are different ways to tackle this. One could be to utilize CombinedLogger from trixi. However, I'm unsure whether CombinedLogger allows for logging frequencies assigned per logged object (e.g. Scalars every iteration and images every Nth iteration), which is a feature I would like to have.

Additional context
Solve before implement logging frequencies as part of #47

[justusschock]

I'd like to address this, once #139 is done, since we can then introduce a logging frequency on our own (without having to hack trixi anymore)