DIY: volume 'bargraph' in html for Sercona preamp

added an outline to the table and a nicer bargraph to the Master volume current value.

 

the tablet on the left had a 'fresh' screen drawn and so there was no 'last button' to re-press. the phone, otoh, had a volume-up button pressed after the screen launched, and so it ungreys to allow the user to press it and get the last action, again, easily.

Done