FORMUS3IC_LAS3 / embb

The priority queue relies on setting an invalid time value for
non-existing nodes. However the time comparison checks for valid
embb_time_t types. Therefore prior to doing the time comparison, the
time values have to be checked for validity.

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.

A blocking binary heap based priority queue for tasks with deadlines has been
added. The priority queue sorts incoming tasks according to their
increasing deadline attribute.

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

On releasing all resources, the node waits for the completion of all
tasks which are associated to a specific action. Since we never
incremented the task counter for actions, this loop spun.

The cmake configuration option HARD_REALTIME was added. This sets or
unsets the compile time variable EMBB_HARD_REALTIME.

# Conflicts:
#	README.md

Merge branch 'embb517_mutex_based_atomics' of https://github.com/siemens/embb into embb517_mutex_based_atomics

mtapi_c: fixed handling of detached tasks in conjunction with retaining queues and multi-instance tasks