Added support for saving current volume. Also adds a rolling volume update every 6 seconds. If the window is minimized, the volume update occurs every 1.6 minutes.

Added basic support for the "Old Tumblr Dashboard" userstyle.

Fixes no slider on the new UI and keeps support for those still using the old UI

Added pop-up menu after clicking on the extension in the toolbar. This menu includes options to:
Hide the slider (until refresh)
Re-add the slider
Quick mute all media (until refresh or slider update)
Reset all media volume to 50%

Prevents extra sliders from being created.

Adds slider to the home page if the user is not logged in.