Define ranges by frequency in var_scale_colmap

[heikoklein]

Is your feature request related to a problem? Please describe. color-scales in pyaeroval are equal for all frequencies. For hourly PM, a range of 0-100 is reasonable, while for monthly PM, the range is rather 0-30.

Describe the solution you would like to see The var_scale_colmap.ini has sections for different frequencies in addion to a main scale.

Additional context This issue has been off-spawned from #1221 since it has no immediate requestor. It might require re-programming in aeroval, too.