Cleanup (pep8)
Implement upgrade step directory scanner.
Implement upgrade step directory directive.
Automatically set profile version to latest upgrade version.
Extend UpgradeStep with ``install_upgrade_profile`` method.
Extend importProfile directive with new optional "handler" argument.
Wrap upgrade step handlers with profile information.
Implement marking installed upgrade steps.
Update gatherer to include orphan information.
Highlight orphan upgrade steps in manage view.
Update translations.
Update changelog.
Bump target version to be a feature release.
reorder readme: move "Import-Profile Upgrade Steps" section down.
Format timestamp versions in manage view.

For improved readability versions based on timestamps are formatted in
a human readable format in the manage upgrades view.
When hovering the mouse over such a version, the raw version is displayed
so that it can be easily copied.
add documentation for upgrade step directories to readme.
Cleanup (pep8)