Added warnings for unused keywords in the detector geometry definition.

Did this by passing along a reference to the header configuration (i.e. the empty section), rather than a full ConfigReader object (as it was only used to fetch the header configuration anyway). This way, the config gets updated when keys are used. Also added check in the individual implant and support sections, and for section names that are not used in the framework.

The MR also fixes a bug with capitalisation, where things failed if one put for example [Implant] instead of [implant].

This fixes issue #278 (closed) , I think.