hw: clearer naming scheme in kernel API

Rename kernel syscall in kernel call and the kernel-API
files in kernel/interface* .

ref #953
hw: use platform-thread pointer as pager badge

ref #953
hw: identify core threads through stack pointer

ref #953
hw: remove Kernel::get_thread

ref #953
hw: simplify Kernel::start_thread

Instead of writing initial thread context to the platform-thread members
and then communicating this core object to kernel, core calls
Kernel::access_thread_regs first to initialize thread context and then
Kernel::start_thread without a platform-thread pointer. This way
the frontend as well as the backend of Kernel::start_thread loose
complexity and it is a first step to remove platform thread from the
vocabulary of the kernel.

ref #953
hw: simplify Kernel::new_thread

Don't set priority and label in platform thread and then communicate this
core object via Kernel::new_thread but communicate priority and label directly.
This way kernel doesn't need to know anymore what a platform thread is.

ref #953
hw: don't provide thread base via platform thread

ref #953
hw: spelling fix in kernel/thread.cc

ref #953
hw: rename delete_thread in kill_thread

ref #953
hw: adjust expected serial start-message in run

ref #953
hw: get rid of Kernel::current_thread_id

Every thread receives a startup message from its creator through the initial
state of its userland thread-context. The thread-startup code remembers the
kernel name of the new thread by reading this message before the userland
thread-context gets polluted. This way, Kernel::current_thread_id becomes
unnecessary.

fix #953