Client library API, client changes. See #4091

alpha release of crabclient library api

Rebase of the client library

minor correction

Client Library: redo logging and create cmdexec

Add class Task for client API

Some pull requests you might look for history:
https://github.com/dmwm/CRABClient/pull/4213
https://github.com/dmwm/CRABClient/pull/4234
Removing the ClientAPI dir. Will be kept in a different repository