this rather large patch changes the way cells are handled in the SS.
It moves RLC and PDCP entities to the cell map of the SS, such that each cell
has its own entities. This allows to support HO operation, for example,
in which two cells need to send SRB messages.
It also extends most of the syssim interface to include the cell name
in all commands so they can be applied on the specified cell only.
this fixes an issue where commands are received out of
order and we are therefore applying configs incorrectly. if
commands include a timinginfo we are now putting the command
on a queue that the SS reads after the start of a new TTI.
the security and cell reconfig commands will be added in another
PR after the AS_security command has been fixed.