Take "out of plan bounds" activities into account in total count display

[duranb]

Resolves #1058

To test:

1. Create a plan and add any number of activities
2. Select an activity
3. Edit the anchor of the activity to be a negative duration relative to plan start
4. Verify that the nav bar now displays a "1" for the activity status.

[AaronPlave]

Interestingly if I anchor an activity to the out of bounds activity from the repro steps the problem count remains at 1 even though the second anchored activity is also out of bounds. Though maybe this is actually coming from the API so no change would be needed in this PR?

Edit: I'm not able to always reproduce this, seems fairly particular. Do see it happening if you have a directive negatively anchored to plan and then anchor another directive to that first one with a positive offset to the parent directive. When you set the offset to negative on the child directive, validation will correctly state that the child directive is out of bounds. But when positive, the validation thinks that child is in bounds.

[AaronPlave]

Filed an issue in aerie related to my comment, otherwise LGTM.

[duranb]

Filed an issue in aerie related to my comment, otherwise LGTM.

Thank you!