Tour Audio Implemented

Implemented ability to specify a URL with an MP3 audio track for a tour, and to set the timings for each tour step, so a step can appear at a particular point in the audio timeline. Additionally provided basic audio controls to play the audio URL provided for test purposes.

As an FYI, I have created a follow-on card to replace the native audio control with a custom UI, so as to adopt the standard ChronoZoom look and feel, rather than go with each browser's own native implementation, which all look different, and also to provide cosmetic improvements to the lapsed time entry with real-time validation.