get_camerah interface

Adde *get_camerah* interface to the *uca_plugin_manager*.
This interface actually allows to pass parameters to the camera that is about to be created, from the Python binding. The old *get_camerav* interface was unable to do that, since it is currently impossible to create a sane GParameter in Python... It is, however, possible to create a GHashTable. So i use that one as a middle layer to build GParameters inside the C-world and pass them to the *get_camerav* afterwards
I will later on need that interface for the kiro camera plugin.