Release twofactor_totp 0.7.3

Reason

PR #232 "Adapt to new login design"
Dependency updates

Product approval
[x] Verify transifex commits are in master: If a folder https://github.com/owncloud//tree/master/l10n exists, then https://drone.owncloud.com/owncloud/ should receive nightly '[tx] updated from transifex` ...
[x] Ping pmaier to check info.xml description and screenshot
[x] Get approval on translations from pmaier - send the date of the last tx commit from drone to Patrick

[x] Create QA Milestone and set the description to $version
[x] Move tickets from milestone development to qa (testplan and tickets mentioned in release ticket)
[x] Create release branch with the format "release-$version"
[x] Create "$version Testplan" #242
[x] copy new/reopened issues from the previous release ticket as 'Issues to review' below.
[x] check if Non-normal Release Process applies, and adapt this checklist.

[ ] Changes in the docs needed? If so create issue in owncloud/docs. -> https://github.com/owncloud/docs/issues/4203

All actions to be done on the release branch from here:

[x] Bump version in info.xml (no version suffix)
[x] Bump "sonar.projectVersion=" in sonar-project.properties (no version suffix)
[x] Check php version dependency in info.xml
[x] Check minimum ownCloud version dependency in info.xml
[x] Change CHANGELOG.md 'Unreleased' to '$version' (today's date)

[x] Ping product owner to create github tag for v${version}-rc1 on release branch (see https://confluence.owncloud.com/display/EN/Product+Owners+List)
[x] Build and sign RC tarball from github tag v${version}-rc1 (see handbook for how to build)
[x] Upload as Github release using changelog entries
[x] Test and document in testplan + manual explorative testing:
- [ ] If this is an enterprise app: Enabling the app must start the grace period
- [ ] If this is the initial release of an app: Check that the minimum version constraint resolves correctly
- [ ] Add section "Changlog Testing" using github releases text or CHANGELOG.md from release branch
- [ ] Do changelog tests
- [ ] Do regression tests
- [ ] smoke test with docker image owncloud/server:latest
- [ ] => Final "Go" from QA (set 'QA-ready' label) => else do another RC after fixing issues in the "release-$version" branch

[x] Upload tarball to marketplace (see handbook in confluence for details)
[x] Publish tarball for customers - old 10, old 10.0 and new portal (see handbook for details)
[x] Send mail to release-coordination with link to this ticket and to the changelog
[x] Copy email to rocket chat #updates channel

[x] Add a new 'Unreleased' section in CHANGELOG.md (and also update links at the bottom!)
[x] Create PR to merge changes back to the master branch with description "Closes #XYZ" with the release ticket number
[x] Rename QA milestone to $version and close the milestone
[x] Update https://confluence.owncloud.com/display/PROD/Upcoming+Releases
[x] Ensure release template is up to date
[x] Ensure the testplan template (community or enterprise) is up to date
[x] Close the testplan issue