FORMUS3IC_LAS3 / embb

The implementation now uses embb_time_t time stamps instead of uin64_t
time stamps. Thereby time checks now rely on embb internals, instead of
more clumsy comparissons.

Furthermore this allows to use the embb::base::Duration on EMBB level
and thus setting _relative_ deadlines, instead of _absolute_ deadlines
on task creation.

The node struct was extended so the scheduling mode can be configured on
Node initialization. Therefore the scheduling mode struct was moved from
embb_mtapi_scheduler_t.h to mtapi.h.

The scheduling mode is now another node attribute and can be set as such
on program setup.

The EMBB layer was extended so tasks now can be started with the deadline
property.

In order to specify a deadline for a task / group of tasks the class
ExecutionPolicy must be instanciated. Here the required deadline may be
set.

This commit adds the deadline attribute to the task attributes struct.
The task deadline is an 64bit value.

Ticket EMBB-349

mtapi: added description of default node attributes in mtapi_c and fixed typo in mtapi_cpp documentation