No data message after navigating back to the summary

[maraf]

After navigating back to the summary, "No data message" is displayed for a second.

1. Summary
2. Navigate to overview
3. Go back.

[maraf]

I think that it is caused by the fact that the view model (and so data context) is set a moment later (maybe in async method) than the page is shown.

[maraf]

Not seeing it anymore.

[maraf]

This problem is now simplified to situation when outcome is created in month which is not included in groups for now, so the groups are cleared and reloaded.

[maraf]

Probably requires #99.