Add ability to change caption begin and end time
Add 3 unit tests for Caption class
Add UserInputEnabled property with enabling/disabling functionality to
CaptionView
Add PlayheadChangedEvent to timeline

Adds the PlayheadChangedEvent to timeline. This will fire every time
the playhead is set by the user on the timeline. The mainform will
then handle the fired event.
Rename OnPlayHeadChangedEvent to OnPlayHeadChanged
Refactor VideoLoaded Event in EngineView

VideoLoaded now uses the EventHandler delegate, added in C# 2.0, as
opposed to a custom event delegate.

Adds race condition prevention EngineView.OnVideoLoaded.
Add CaptionTimestampChanged event to Timeline

Adds the CaptionTimestampChanged event to Timeline, which is invoked
everytime one or more Caption Timestamp (Begin, End, or Duration) are
modified in the timeline.

The event is handled by the main form so that it can update the
CaptionView's displayed value to the current value.