Minor cleanup of code and comments

[jougs]

This is stuff that was lying in my cleanup branch and I don't want to be lost. See the list of commits for what and why.

[heplesser]

Hi @jougs! Thanks for these fixes. I agree with most of them, and also with moving register_* calls out of nestmodule.cpp. But I think the *_managers are not the right place for them: The managers take care of NEST parts, but they do not define which parts NEST has. With the new modelsmodule, this definition of what is part of NEST wrt neurons and synapses has become nicely separated, and ideally conn-builders and growth rules should be handled correspondingly. I see three options in no particular order and enumerated only for ease of reference:

1. Leave the register_ calls where they are right now until we find a good place for them.
2. Call register_conn_ from conn_builder.cpp and register_growth_ from growth_curve.cpp (provide registers components).
3. Add the register_{conn,growth} calls to the auto-generated modelsmodule.cpp and maybe call that register_nest_components.cpp then.

[jougs]

@heplesser: I agree with all you say. Also, the code does not link properly as it stands. Given the situation I'm in, I'm afraid I won't be able to do anything about this anymore. Please feel free to take the changes, modify the code in whatever way you see fits, or discard them. I just wanted to get these off my chest.

[heplesser]

@jougs If you could reset the connection_manager.cpp, nestmodule.cpp and sp_manager.cpp in this PR, I'd be happy to approve it :).

[jougs]

Done.

[heplesser]

@jougs Thanks!

[heplesser]

Minimal code tidying, thus merging based on single review.