WIP: Extend telescope interface to support dp3
everybeam::Load loads a MS and returns a Telescope class matching the telescope found in the MS. This is used by wsclean but can be convenient to use in DP3 as well. Currently DP3 directly calls ReadStation directly to load Station. This MR makes it possible to use everybeam::Load instead, by extending the Telescope class needs to give access to the underlying stations.