Dvc

1) [Fix bug where wdir was not converted to unixpath when saved to a dvc file](https://github.com/iterative/dvc/issues/1721);

1) Warn when there is no cache locally or on the remote;
2) Fix NotDvcRepoError message;
3) Ignore cryptography's warnings caused by paramiko;
4) Fix posixpath/ntpath mixup in ssh remote driver on windows;

1) Support choosing between `list_objects` and `list_objects_v2` for s3 remote using `listobjects` config option;
2) Use decorator for cleaning up gitignore on error and reminding to add to git;
3) Fix bug in dvc state where inode wasn't converted to sqlite format properly;

1) Fix the message for dvc file formatting error;
2) Support `-f|--file` for `dvc add`;
3) Fix bug in ssh remote driver on windows;

1) Fix stage checksum calculation when `wdir` is default;

1) Multiple test improvements;
2) Fix a bug in `dvc repro`, when callback stages were not reproduced and instead a build cache was used;
3) `dvc status` with `--remote` now implies `--cloud`;
4) Raise exception when output/dependency doesn't exist. Previously this was handled properly only for local outputs/dependencies;
5) Use temporary file as an intermediary step when uploading to ssh remote to prevent cache corruption;
6) Use cache directory mtime/inode/size to do cache validation faster;
7) Support `dvc run --wdir` as a way to run dvc file command from a directory that doesn't match dvc file location;
8) Gracefully handle a case when a progress bar is interrupted with a prompt;
9) Support `dvc add` for symlinks that point to a location within or outside the current project;
10) Multiple code refactorings;