Support for docker registries

In this issue support for docker registry will be added.

Following registries will be handle:

• GitLab registry
• Dockerhub

In this issue also three small fixes/futures will be done:

• rendering changelog when section Unreleased is empty

  When section Unreleased is empty autoupdater puts new subsection after one blank lines and do not add extra empty line after it

• updating projects when webhook is not defined

  when update methos is called it returns generator which is then used to notify on rocketchat, it just requier to list updated projects generator

• filtering projects to update by checking user role in project

  in gitlab there are a lot of public projects, if some of them will have autoupdater.yml file it will try to update them even if it is not a user of it, it can be fix by filtering project by assess level