Add minimum elevation check for CMB and Calib blocks

[mmccrackan]

Added a check for whether CMB and calibration blocks are above the sun avoidance minimum elevation. An assert error will be thrown if any blocks are too low. This is added before gap blocks or moves are calculated, which should all be guaranteed to be above the minimum elevation anyway. Block division or merging shouldn't affect things either.

Intended to address #107.

[mmccrackan]

I didn't notice #108 when I first pushed this, but that was closed and not merged, so I've taken a few pieces from that and incorporated them here. I think the min_el comments in #108 have been addressed due to the addition of parts from the dev branch that allow build_ops to have access to policy parameters.

[kmharrington]

Looking at this, it bothers me a little that we're using the sun avoidance policy as the place to set the elevation limit. The elevation limits come from settings in the ACU, same as the 'az_limits' in the 'plan_moves' config.

The sun avoidance calculator might also need to know how low the telescope can move in elevation, but the limit is broader than just sun avoidance.

[mmccrackan]

Looking at this, it bothers me a little that we're using the sun avoidance policy as the place to set the elevation limit. The elevation limits come from settings in the ACU, same as the 'az_limits' in the 'plan_moves' config.

The sun avoidance calculator might also need to know how low the telescope can move in elevation, but the limit is broader than just sun avoidance.

Okay, I separated them to match the az_limits dict for now and added an upper limit for completeness/sanity checking. I made it so it will always be a required input unlike az_limits since they might change.