fixed bugs in and improved several aggregation options

- aggregation options 'dailySWPextremes', 'dailyTranspirationExtremes',
'dailyTotalEvaporationExtremes', and 'dailyDrainageExtremes',
'dailyAETExtremes': adapted that the mean instead of the first of
multiple extreme days is used
- aggregation options 'dailyTranspirationExtremes',
'dailyTotalEvaporationExtremes', 'dailyDrainageExtremes', and
'dailyAETExtremes': fixed a index bug in the header
- aggregation option 'RainOnSnowOfMAP': added SD
- aggregation option 'dailySWPdrynessIntensity': added mean of the
amount of dry-period missing water, as well as the duration and the
number
- fixed bug in aggregation options
'dailySWPdrynessEventSizeDistribution' and 'dailySWPdrynessIntensity':
used xx.dy.all instead of xx.dy (yearly aggregations are based on
xx.dy-formatted data)
- generalized functions 'start10days' and 'end10days' (only used in
aggregation option 'dailySWPdrynessANDwetness'), i.e., removed
exlcusion of dry periods in first 90 days, generalized from fix 10 days
to n days periods; replaced with 'startDoyOfDuration',
'endDoyAfterDuration'