add array preview listbox to Data Array View

The listbox shows lines for all indexes in the first dimension of the ndarray and up to 100 columns for the second dimension.

See merge request !8

The listbox shows lines for all indexes in the first dimension of the ndarray and up to 100 columns for the second dimension.

Call pure transformation in an activity rather than execute in current transaction. This way we split ingestion part from transformation part.
Note: this commit will serialize argument_list to activity's mysql table in case of big packets this can be slow, in case of small appends it can be acceptable.
Instead we should call with start and end offset only and data should be read from Data Stream itself (WIP).

Raise in case of improper server side configuration so sender is aware rather than silently return nothing and fool sender it's all ok.
Pylint.

Remove an example that stored twice the RAM memory zeros in ZODB's root as this can quickly run out of space any Wendelin instance.
Use ERP5-ish API to work with Data Arrays

4dfcdc5f (DataArray: get array slice by HTTP Range Request) added HTTP
range support for DataArray by way of copying code from ERP5's BigFile
implementation.

It is better to not copy the code and just use the base class and hook
into it in a proper way (I think it is possible to do even without
mixin).

Add a proper FIXME/TODO so we do not forget to fix it one day.

/reviewed-by @Tyagov
/cc @klaus

DataArray: get array slice by HTTP Range Request

See merge request !5

Allow to pass additional keyword arguments to transformation script

See merge request !4

Conflicts:
	bt5/erp5_wendelin/SkinTemplateItem/portal_skins/erp5_wendelin/DataStream_transform.xml

A simple example of a map reduce job that stores intermediate result to an Active Process and calculates average on slices of a ZBig Array.