WIP: Rtapi cleanup v2

[hdiethelm]

Continuation of #3908 reverted in #3918

Target: Move some classes out of the huge uspace_rtapi_app.cc

uspace_rtapi_main: Contains the main function and helpers
uspace_rtapi_app: Contains the RtapiApp class
uspace_posix: Contains the PosixApp class

Other fixes:

• Don't start master just for exit: 371793c
• Remove unused rtapi_task::ratio: 3097578
  • Set but only read to force a fixed ratio which probably was not the intention
• Slightly different lock to avoid needing reference to instance: c8af827
• All real time implementations are now library's and handled the same way: 62e5ea6
• No hard-coded library paths e1bbaf4

[hdiethelm]

Still open:

• libuspace-xxx.so.0 -> liblinuxcnc-rtapi-xxx.so ?
  • Longest name would be liblinuxcnc-rtap-xenomai-evl.so.0
• Check if slightly different lock to avoid needing reference to instance: c8af827 is a good idea
• Review

And

In the Submakefile it reads:

$(call TOOBJSDEPS, $(USPACE_POSIX_SRCS)): EXTRAFLAGS += -pthread -fPIC

Shouldn't that be (not adding to EXTRAFLAGS):

$(call TOOBJSDEPS, $(USPACE_POSIX_SRCS)): EXTRAFLAGS = -pthread -fPIC

Hmm, I don't understand makefiles in depth. I just copied what was already there a few lines below and edited it to match my lib. As much as I understand this, it just adds this flags to the global EXTRAFLAGS in Makefile for one compile command only. I did not see any duplicated flags.