Dvc

* plots: clean up template anchors and collection (4061) Suor
* trees: handle tree.walk errors the same way as os.walk (4059) pmrowla
* fix url signing when using GoogleStorage on GoogleComputeEngine (4057) bgheneti
* cache relpath on stage (4053) skshetry
* optimize: remove `fsync` when dumping rwlock data (4052) skshetry

* get-url/import-url: save dependency before downloading (4049) efiop
* remote: rename "checksum" -> "hash" (4051) pmrowla

* plots: add smooth template (4046) pared

* plots: make sure template is using data anchor (4045) efiop
* plots: modify: handle --unset for nonexistent options (4044) efiop
* remote: continue remote/cache/tree refactoring (4041) pmrowla
* Performance improvement of dvcignore (3967) karajan1001

* (bugfix) get/import: fix broken progress bar (4039) skshetry
* metrics & plots: help output improvements (3963) nik123
* gdrive: add open (3916) casperdcl
* snap: make future major version upgrades easier (4038) casperdcl

* run: maintain order when -f/--force overwrite stage (4035) skshetry
* metrics: diff: introduce --precision (4026) efiop
* fix error message on dag.py (4036) skshetry
* bugfix: `get` dump folder contents in respective output folder (4034) skshetry
* schema: provide a jsonschema for dvc.yaml (4028) skshetry
* plots: fix handling of multiple plots from single revision (4031) pared
* tests: unittests for dvcfile and some small fixes (4032) skshetry
* remote: separate cloud remote and cloud cache classes (4019) pmrowla
* remote: use separate working tree instance for local cache (3991) pmrowla
* 4021, do not make config directory world writeable (4022) bjonnh