Use full classpath for component class loading

Last feature before RC.

Change the way MORSE load classes. fixes #247
Use a new property classpath instead of Class and Path.

```
# before
my_own_camera.properties(Class='MyOwnCamera', Path='module/in/my/pythonpath')
# after
my_own_camera.properties(classpath='module.in.my.pythonpath.MyOwnCamera')
```

Use standard method `create_instance`.
Remove duplicate code for class loading …
While here, use full-classpath as key for services instead of just classname.