Color code playback calendar SD card

maybe-later
#1

when viewing playback, the timeline shows when an event was recorded in blue. when you open up the calendar to select a specific date, it would be great if the days of the month were highlighted if there were any events recorded that day. Currently all the days just show as white other than the current date and the selected date. This feature would enable users to know how far back their recordings go without blindly going back a day at a time and then checking the timeline for any blue sections.