fixes #3 Adds support for getting a URL to a stream (or parts of) in multiple ways. The app menu enables getting a URL to the current stream, the current segment being played in a stream, or the current playback location in the stream. Firefox adds an item to the browser's context menu for every segment to enable getting a URL to any segment. Similarly, an item is added to the context menu for the progress area to enable getting a URL to any non-current location within the stream. On pause, the URL is updated to match the current stream location so if the page is reloaded for some reason or the browser is closed and the tab reloaded at a later date the app starts back where it left off. Unfortunately a quick search seems to indicate changing the hash in the beforeunload event may not work so this behavior cannot be automatically done if the browser is closed while still playing. history.replaceState can be used, if supported, to modify the last value but it seems useful to leave the history intact in case the app later supports hashchange events and uses them to skip back in time or around the app.