merge 'parameters' and 'commands' to 'accessibles'

- for now, the definition also accepts the old syntax
  (to be changed later)
- Commands have datatype CommandType
- do not need keyword for the decription parameter of Override
- issue a Warning when a Parameter is overwritten without Overrride
  (this should be turned into an error message)
-

Change-Id: Ib2c0f520abb5b4d7e6aed4d77a0d2b8bc470a85a
Reviewed-on: https://forge.frm2.tum.de/review/18251
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

etc/epics.cfg

@@ -17,11 +17,11 @@ framing=eol
 encoding=secop
 
 [module tc1]
-class=secop_demo.demo.CoilTemp
+class=secop_demo.modules.CoilTemp
 sensor="X34598T7"
 
 [module tc2]
-class=secop_demo.demo.CoilTemp
+class=secop_demo.modules.CoilTemp
 sensor="X39284Q8'