The drop down for plot types should only contain plot types that can
be combined. The reason is, that we can only draw images with two
x/y-axis. Therefore a combination of types that would need three or more
axis is not supported.
The writerCache in DataStore did not use the partitionId
in its cache key. Therefore the cache could return the
wrong writer and events were written to the wrong
partition.
Fixed by changing the cache key.
andi