Dvc

* py3: remove string compat related code (3024) mroutis
* py3: get rid of is_py checks (3021) mroutis
* py3: remove future imports (3022) mroutis
* py3: deprecate 2.7 (3019) mroutis
* tests: func: convert test_get.py test_utils.py to new fixtures (3014) efiop
* repo: move dvcignore from repo to tree (2974) pared
* dvc: make graph consist of stages not their paths (3012) Suor
* dvc: support granularity for fetch/pull/push/status/checkout (3002) efiop
* Improve Google Drive auth failure error reporting (2991) MaxRis
* summon: first draft with python specific implementation (2971) mroutis
* ui: fix extra newline in dvc version (3006) Suor
* test: test ignore nuances (3003) Suor

Fix `inflect` version.

* dvc: use ' to mark dynamic command output, et al. (2986) jorgeorpinel
* tests: use dir_helpers on repo (2950) mroutis
* tests: use dir helpers on updater (2952) mroutis
* import: test: refactor to dir helpers (2935) pared
* ui: reorder checkout options to go from common to rare (2966) Suor
* remote: s3: adjust jobs number basing on file descriptors number (2866) pared
* import: allow downloading regular files/dirs tracked by git (2889) Baranowski
* Standardize gdrive tests with others remotes (2958) MaxRis
* temporary_windows_drive fixture: move to dir_helpers (2937) pared
* tests: use dir helpers on analytics (2951) mroutis

* Restyle remote: use absolute from root for gdrive credentials file (2949) e3bo

* remote: make `copy` links atomic for local/hdfs/ssh (2943) efiop
* dvc: add checkout --relink (2922) Suor

* remote: Extend S3 remote support for custom ACL (2931) rbvesb