[TRIVIAL] Implement OSyncCapability Parameter

[dgollub]

The OSyncCapability parameters are not implemented. The API functions are just stubs and don't do anything:

• osync_capability_add_parameter
• OSyncList *osync_capability_get_parameters(OSYncCapability *) TODO
• osync_capability_set_parameter (marked as deprecated should get dropped)
• osync_capability_get_parameter (marked as deprecated should get droppped)

This is a trival ticket since the OSyncCapability code is not very complex.

Additionally the XML assembler/parser of OSyncCapability needds to be extended to handle Capabilty Parameters:

• osync_capability_parse_child
• osync_capability_assemble