Fix wav header and mime type, add playback time to record callback, add types

[niklasdahlheimer]

This pull requests

fixes:

• wrong mime type for blob (audio/wav instead of audio/mpeg)
• wrong wav header: riffChunkSize was hardcoded to 52 byte, but should represent total file size - 8 bytes (see specification ) and make it better readable by extracting variables

adds:

• missing types (lots of any types replaced by actual type)
• playback time to record callback: maybe there is a better way to handle this, but some sort of current recording time should be available