feature: explicit representation of an exescript (batch)

[shadeofblue]

currently, WorkContext is connected to an activity and commands are sequentially added to it until they're committed (sent for execution).

this causes two issues:

• side-by-side execution (and even preparation) of scripts is impossible since - because the context is the same - the scripts will interleave each other
• implicit deploy: currently, deploy/start are added implicitly when the first script is started -> there could be a lock which would only trigger on the first sent script (and not necessarily on the first started one)

we would like to extract the Script/Batch class from the WorkContext and make it explicitly separate -> the WorkContext would still be bound to a single activity but the batches would not be part of WorkContext itself