added absolute and relative thresholds for IVT detection

[jobo95]

Hi,

I just added the parameters IVTthresholdAbs and IVTthresholdRel to the moaap function:

• IVTthresholdAbs is the same absolute threshold value as before
• IVTthresholdRel is an array with monthly threshold values for each respective grid point ( e.g. calculated via percentiles). It can be used in addition to the absolute value. Default is None. It's supposed to have the same spatial dimensions as the input IVT field (shape (12, lat.size, lon.size)), where e.g. [0,:,:] is the threshold field field for January.

Bests Johannes