Possible bug if model location is set but language and mapping are not

[reckart]

If a component uses some mapping e.g. for constituents or POS tags, there might be a
problem if a model location is explicitly set but neither language nor mapping location
are set. The component will probably fail to load the mapping.

- it should be possible to disable mapping entirely
- it should normally not be necessary to set the language if a model is specified explicitly
- if under a given circumstance an optional parameter becomes mandatory, a proper exception
with a useful error message should be generated

Original issue reported on code.google.com by richard.eckart on 2015-02-24 13:23:27