visualTimeline.java
-Fixed bug where timestamps were not being reset when slides were being cleared.
-Consolidated various timeline index calculations into single getTimelineIndex() method.
-Clearing slides resets all VisualItem tags and display times.

Quickshow.java
-Updated method calls for retrieving selected VisualItem from visualTimeline and passing VisualItem to PopupDialogue.

PopupDialogue.java
-Added instance variable to track the timeline offset of a VisualItem.
-Modified togglePopup() method to accept offset value.
-Tag times account for timeline offset.
-When saving a tag, it will always be the only tag associated with the VisualItem.