Improve plots

[SabineHaas]

changes in this PR

• adapt xticks (no rotation, visual for every subplot)
• remove year from xticks

[SabineHaas]

Thanks a lot @MaGering :)

I cannot accept as I cannot be requested as reviewer in my own PR :D

[SabineHaas]

Ah, I've just realized that for the plot where the whole year is shown, this doesn't work. There are far too many entries:

[MaGering]

Ah, I've just realized that for the plot where the whole year is shown, this doesn't work. There are far too many entries:

I've fixed that with commit c82529e and 67a8839. The AutoDateLocator takes care now of correct labeling.