app_solar: Make MPPT algorithm faster and more stable

[andrewgreenberg]

Right now, the solar modules work just fine, but they are (1) slow to reach MPPT and (2) tend to brown out and reset if the load changes to quickly.

1. Investigate ways to increase the speed of the P&O algorithm so it gets to the MPP sooner. This could be speeding up the tracking loop, or making the step size larger, or whatever. Note: We looked at an INCCOND algorithm originally, but it's just too noisy of a system for this to work well (we think). But the algorithm itself could be looked at again.
2. If we're at the MPP, and the insulation gets less, the solar module tend to brown out and reset. This looses precious time generating energy while in the sun. Make the algorithm better at dealing with suddenly changing levels of isolation.