Add option for reverse play

[TomW1605]

Describe what you are trying to accomplish and why in non technical terms
I want to be able to play history events in reverse so that I can find where something started or an object entered the frame if the detection missed it

Describe the solution you'd like
add a reverse play option to the web interface

Describe alternatives you've considered
at the moment all you can do is jump back and let it play forward. this makes it a lot harder to find a specific moment. and is particularly annoying when on slow internet where a jump will make it load for a long time where a reverse play will allow it to buffer cleanly

Additional context
this is a pretty standard feature of most NVRs and security systems (at least all the ones i have used) so adding it to Frigate would be a significant step to matching commercial offerings