[src/Metadata.hpp] fix shadow warning

should not harm.

the fix came up while looking at the naming of the [struct Component](https://github.com/marvin2k/tools-orogen_metadata/blob/master/src/Metadata.hpp#L24) -- which causes a warning from idl because it is a reserverd corba-keyword:

    .../base/orogen/std/.orogen/typekit/transports/corba/stdTypes.idl:24: Warning: Identifier 'Component' clashes with CORBA 3 keyword 'component'

Would _struct ComponentObject_ be a good replacement?

Signed-off-by: Martin Zenzes <martin.zenzes@dfki.de>