Multisensor Code Ready for Testing

[timburke]

I revised and updated the multisensor code. The current version has changes to make it more robust. It differs from the previous version in the following ways:

• It counts the total amount of water that has passed through the flow meter (i.e. it functions as an accumulator). It does this by sampling the flow rate for 0.1 seconds every 4 seconds.
• It sets up a callback currently every 1 minute to report the accumulated flow in the past minute. It corrects the flow rate for the fact that it is only sampling 1/40th of the time so it multiplies the count of pulses that it has by the ratio of the total time it's reporting for / its on time.
• It has verified sleep power consumption of 30 uA and run consumption of 4.6 mA. This is detailed in Issue #112. The average consumption is ~150 uA, which would translate to almost 300 day runtime (without counting GSM transmission consumption).

This is for review, comments and testing. It needs to be squashed for merging.

[amcgee]

Should the mib12_reflash changes be included here?