Added new endpoints to return plug-ins & versions

[nic-burgers-arup]

These endpoints return (sorted) dictionaries of plug-ins and their versions for both the running instances of Rhino and Grasshopper, as well as those used in a supplied GH file (examined using the GH_IO library). There is one assumption baked into this code: that it is satisfactory and desirable for the assembly version to be returned if the actual plug-in version is blank/empty/null.

[nic-burgers-arup]

These endpoints are useful in certain circumstances that can occur in large organisations, such as: there is a shared set of Rhino Compute instances running and a separate cohort of GH-authors want to run their files on the compute server, so they would like to check if the plug-ins they use are supported by the Rhino Compute instances running in their organisation.