[ux] Don't automatically hide the calendar

[hizkifw]

When viewing the topology graph from the edit screen, the user can choose to view a snapshot of the graph from a certain date by clicking on the date field on the lower right. A calendar will pop up, as seen in the screenshot, however it will disappear after choosing a date.

It would take less time comparing different dates if the calendar doesn't automatically close. The user can just click on a different date without having to click on the date field again. If the calendar hinders the view, the user can simply click out of the calendar area and it will close. Optionally, add a close button to the calendar.