Change component loader behaviour to consider a component found on first valid path

[francisco-miguel-almeida]

Fixes issue #161.

[meyerj]

For reference: This PR implements what has been proposed in #161 (comment).

It would be an option to simply load a package from the first path found in ComponentLoader::importInstalledPackage(). This should fix the overlay semantics of the import() operation and would not break the component or typekit overwrite behavior of a subsequent import call of another package.

So if a package exists with the same name in multiple directories in the RTT_COMPONENT_PATH (e.g. catkin overlay and underlay), only the first one is imported (prefer overlay). If packages with different names provide component types, service plugins or Orocos types with conflicting names (e.g. name clashes or renamed package in one workspace), the inconsistent overlay semantics described in #161 (comment) still apply.

[meyerj]

LGTM, thanks!