This patch moves details about the stack allocation and organization
the base-internal headers. Thereby, I replaced the notion of "thread
contexts" by "stacks" as this term is much more intuitive. The fact that
we place thread-specific information at the bottom of the stack is not
worth introducing new terminology.
Issue #1832
This patch removes the SIGNAL service from core and moves its
functionality to the PD session. Furthermore, it unifies the PD service
implementation and terminology across the various base platforms.
Issue #1841