querying kernel execution status

currently there is no way of knowing how far advanced a kernel is in its execution. =>

[ul][li]add a method to query how many work-groups (and work-items, if possible) have finished execution[/*:m:hkhf5sf5][/ul][/li]

this should be useful in giving user and developer :wink: feedback on how long he/she still has to wait (especially for long running kernels) or to notice infinite loops or execution stalls.