Generalize x_orientation concept

[jpober]

x_orientation keyword might need some adaptation to support arrays where the dishes steer/rotate.

[bhazelton]

Proposal is to not do away with x_orientation but instead to add information that can be per-antenna (length Nants_Telescope). Idea is to put all the antenna based info (including antenna_positions, antenna_names, antenna_numbers) + new stuff (e.g. mount_type) on a Telescope object that becomes an attribute of UVData, UVCal & UVFlag objects with getattr handling so the antenna based info can still be accessed directly from UVData.

[bhazelton]

linked to #1095