Use Version for all Helm versions
The classes HelmGitlabVersion and HelmChartVersion were subsets of the Version class, only changing the accepted input format. But having all these (almost identical) version classes is confusing, and it's easy to use one when you meant to use the other.
This commit removes HelmGitlabVersion and HelmChartVersion, and replaces their usage with using the Version class instead. This simplifies the decision as to what version to use, and makes it impossible to use the wrong version.