l4_capability_control works well for almost all system calls
using a buffer pointer to the capability that it operates on.
Only for sharing/granting of capability lists, it is yet to be
decided how to provide a grant target id.
Thread ids now contain their container ids in the top 2 nibbles.
Threads on other containers can be addressed by changing those
two nibbles. The addressing of inter-container threads are
subject to capabilities.
Task ids are now unsigned as the container ids will need to be encoded
in the id fields as well.
For requests who require even more comprehensive id input, (such as
thread creation) also added is the container id so that threads
_could_ potentially be created in other containers as well.
