(re)capture lost data in ouputs

[cmgosnell]

lots of the data points in the outputs are lost to NaN's and we can smooth some of that out. This will allow us to preserve many many more data points in the master unit list:

• [x] Allow averaging over good months for annual MCOE calculations [pudl issue](Allow averaging over good months for annual MCOE calculations)..
• [x] stop dropping NaN's in the MCOE output pudl issue
• [x] if records do not have ownership % in the ownership_eia860 table, right now we just don't include these records in the compiled outputs... (examples: plant_id_eai 143, 260 and 3). We could assume that the operator of the plant is the full owner.
• [ ] I'm not sure we can actually deal with this, but there are many gas plants which don't have sufficient information in the EIA records to assign them a unit id. Because many of the calculated fields depend on the unit it, we are loosing records this was as well.

[cmgosnell]

on the generators without unit_id_pudl, there are less than 100 generators that do not have unit_id_pudls but do have info in 923. If there is no 923 data, it really does not matter if there is no unit id because everything dependent on the unit id (fuel cost, heat rate, etc) depends on 923 data.