Keep time range constant when changing time range in PI Vision

PI Vision should keep the time range constant when changing the end time in a display. The current behavior (verified with tech support) is: - If the end time is * (now), one can type a valid timestamp in the end time box and a start time is calculated based on the current default span, such as -8h. - If the end time is not *, and has a timestamp string, when the string is edited and the user hits enter, the edited time is copied to the start time and the end time value prior to editing persists. This causes two significant issues: 1) Behavior of the display is significantly different based on how the starting point for the user. 2) If the user is researching a problem that happened in the past, this could cause PI Vision to try to return a large timespan of data, locking the PI Vision display and potentially creating communication errors with the server. In both PI Coresight and PI ProcessBook, time span was always respected if the user changed the end time. The behavior of PI Vision is a significant departure from what is expected from a time-series visualization tool.