v2 Blocking Bluetooth Sockets with Select

using a select() statement with a 60 second timeout instead of relying on a timeout of the read call and a sleep statement has reduced CPU usage significantly. Example PiZero CPU usage reduced from 26% to 1%. Pi3b CPU usage from 15% to less than 1%.

SVG creation now properly accumulates and averages data into appropriate buckets instead of using point in time values for each level of granularity. Daily graphs have a 5 minute granularity/average. Weekly have a 30 minute granularity/average. Monthly have a two hour granularity/average. Yearly have a 24 hour granularity/average.