Dvc

* Rename --xlab to --x-label, X_TITLE to X_LABEL, same for y (3948) Suor
* plots: fix error when there are no plots in repo (3940) efiop
* dvc: require `--external` for external outputs (3929) efiop
* remote: separate tree functions from main remote classes (3931) pmrowla
* remote: modify: fix --unset (3939) efiop
* Fix quadratic behavior in Repo._collect_stages() (3932) Suor

* dvc: remove `dvc metrics add/remove` (3928) efiop
* refactor: rename utils.stage to utils.yaml (3923) skshetry
* Fix modifying plot (3926) Suor
* bugfix: rerun stage when command is changed (3922) skshetry
* dvc: replace `pipeline` with `dag` (3905) efiop
* Implement removing of the stage (3881) skshetry
* dvc: rename "working tree" to "workspace" (3914) efiop
* dvc: rename `dvc lock` -> `dvc freeze` (3915) efiop
* Add plots props and `plots modify` params (3911) Suor
* use fork of mockssh-server (3910) skshetry
* pre-commit: don't run dvc in parallel (3912) efiop
* use `selectors` instead of `select.select()` (3899) skshetry
* Update bug report template (3903) jorgeorpinel
* tests: make ssh_server session scoped (3898) efiop
* dvcignore: use correct root .dvcignore for subrepos (3895) pmrowla
* plots: replace --show-json with --show-vega (3891) efiop
* Bugfix: _credentials_location (3896) nickdelgrosso
* brancher: only yield git revisions that contain repo_root (3883) pmrowla
* modify issue template (3887) skshetry

* dvcignore: fix bug in subrepo detection (3880) efiop
* run: raise error when command is not specified (3850) skshetry
* ignore: CleanTree should always check ignores, not just for walk() (3876) pmrowla
* addressing: allow stage name addressing without ":" (3842) skshetry
* run-cache: don't forget to set wdir (3873) efiop
* state: always use working trees (3871) pmrowla
* log: reduce log, make it readable/easier (3834) skshetry

* optimize local status (3867) efiop
* Auto-completion of the `dvc remote rename` command (3868) karajan1001
* snap: release non-stable-semver tags to beta (3865) casperdcl
* test: fix hdfs/azurite/oss tests (3864) efiop
* tests: unit: azure: add etag test (3862) efiop
* azure: support external file dependencies (3852) steffansluis
* dvcfile: serialize params on --no-exec (3859) efiop

* remote: local: protect uploaded files (3858) pared
* azure: drop obsoleted url format (3856) efiop
* plot: fixup for template help message (3854) pared
* external_repo: use RepoTree for fetch/import/get (3841) pmrowla
* dvc: add: set top level md5 to None (3846) efiop
* params/metrics: introduce --no-path and --old (3845) efiop
* dvc: don't write default values for cache/persist/metric (3844) efiop
* plots: point template help info to manual (3830) pared
* run-cache: don't forget to account for params (3843) efiop
* plots: remove --select CLI option (3840) efiop
* (OutputAlreadyTrackedError): Add git suggestions to stop tracking files (3808) PuneethaPai
* remote: support saving RepoTree objects directly to cache (3825) pmrowla
* repro: fix help message for default target (3831) skshetry
* dvc : renamed --outs-only to --dvc-only (3797) growupboron
* logger: add trace, count --verbose/--quiet (3806) casperdcl

* remote: is_dir_checksum: handle empty/None checksum (3836) efiop
* Add a new rename command (3794) karajan1001
* lock: make froze message clickable (3833) pared