Add support to write to persistent storage SD?

[usaguerrilla]

We want as much space as possible. As we want to collect data often and a lot of it. This will include all sensors data.

• choose parts (SD, FLASH, EEPROM?), > 10M? Needs discussion.
• PCB design

[usaguerrilla]

For some date we need around 2-3 hours storage. For small subset we might need 12-24 hours storage.

[usaguerrilla]

Also some data will have higher sampling rate than other.

• GPS -> once a second or so
• Accelerometers -> 10-100 times a second
• Temperature -> once in 1-15 seconds We can use binary storage if we are tight on space.