Handle missing summarized cost entries

If costs isn't activated for subprojects the summarized cost entries are
missing in the API response for the current project's work package.
Merge pull request #116 from finnlabs/hotfix/handle_missing_summarized_cost_entries

Handle missing summarized cost entries
Test fractional hours
Split fractional hours in hours and minutes
Merge pull request #118 from finnlabs/hotfix/17228_handle_fractional_hours

17228 handle fractional hours
Adapt version to corresponding OpenProject core version.
Adapt version to corresponding OpenProject core version.
Update stable to v4.0.4