Added custom myExperiment alternative, Changed Taverna migration action to make use of semantic annotations for #166

* Copied SSH taverna migration service to plato module
* Changed migration service to use semantic annotations
* Changed migratino service to adhere to migration profile
* Updated WorkflowDescription to require explicit method call for parser to avoid parsing in getter
* Added UI to create alternative from myExperiment URI
* Changed css to fix background of disabled buttons