Low level improvments

some more scraps from the scatter shot PR. In addition to the patches requested, I added the one which changes the  	Well(Injection|Production)Properties code to the coding style of the module (and for the public API to the conventions also used by the rest of OPM).

This PR has some fallout in other modules, so merge sychronously...
> What possible reason do you have for this change?

consistency with the stupid convention used in the remaining ~500kLOC of C++ code of the project?