release finish: Fix the order of actions

The release branch was being deleted before the reviews were submitted,
which caused that in certain cases the release branch got deleted and
then the submitting step failed, leaving the reviews open without any
release branch existing.

This has been fixed by doing merge -> submit -> delete -> push.
Finished feature 72958770/submit-then-delete-release.
release stage: Do not leave garbage in the tree

In case of CircleCI integration, release stage was using only git reset
--soft, which could lead to leaving garbage in the working directory.

The code was changes to first check if the repository is clean, and if
that is the case, reset --hard is used instead.
Finished feature 73618758/stage-leaves-changes-in-wd.
feature finish: Handle UTF chars in RR description
Finished feature 73378756/fix-unicode-in-review-desc.
release stage: Make sure the release branch exists
Finished feature 72251988/staging-non-existing-release.
release start: Track the pushed release branch
Finished feature 71667054/release-branch-not-tracking.
bugfix: Variable name typo
README: Mention wontfix and dupe labels
release finish: Actually use args.keep
Finished feature 72958770/submit-then-delete-release.
Fix syntactic errors
Finished feature 72958770/submit-then-delete-release.
Bump version to 1.4.1
Finished release 1.4.1 (merge into master)

Conflicts:
	gitflow/__init__.py