Complete rewritten release

• Changed the used the default kirbytext tag from audio to audioext. It's is possible to reactivate the audio tag support.
• Changed the name of theis extension from "Audio" to "AudioExt". "AudioExt" stands for "Video Extended".
• Changed the used custom config variable for a better usage with other extension and kirby.
• Moved the used code into a custom class for better reusage in themes and other extension.
• Some Options and there values are changed.
• Add to the figcaption a CSS class to realize if the tag is at the top or bottom.
• Clean up