Arcpyext

- Made `arcpyext.publishing.convert_toolbox_to_service_draft` compatible on Python 2 and 3

- Removed `convert_service_draft_to_staged_service` function, now has little utility with SD Draft models being moved out to `agsconfig`
- Cleaned up opening/closing of map documents when converting them to service definition drafts

Lots of breaking changes at this release:
- Library now works across both Python 2 and 3 (i.e. ArcGIS Desktop and ArcGIS Pro)
- All SD Draft editing has been moved out to [agsconfig](https://github.com/DavidWhittingham/agsconfig).
- List document datasources has been re-worked into a describe function for maps that works more consistently across ArcMap MXDs and ArcGIS Pro projects. This function is currently quite limited (e.g. it can handle layers that have feature classes as a source, tables, possibilty some other types, but will certainly not work correctly with any service-based layers). Hopefully support for more varied layer types can be added over time.

Bug Fixes
- Allowed switching data sources on a map document from Enterprise GDB's to File GDB's and stripping schema in the process without having to explicitly name the dataset

Bug Fixes
- Fixed an issue with setting capabilities on service extension types

New Features
- Extended list layers to get service layer ID where available
- Add map document compare function (useful for comparing different versions of a document for changes)
- Added monkey patch to arcpy to fix missing 10.4 version when saving a copy of an MXD