Add warnings (or errors) for buy all-sell all and BTM batteries

[brtietz]

Describe the bug

The buy all-sell all utility rate option is designed to simulate two meters: e.g. a facility purchases energy to meet it's load on one meter, and sells renewable energy on a 2nd meter. This does not make sense for behind the meter batteries, where the purpose of the battery is to offset the load. Currently the battery buys energy on the load meter and discharges on the production meter (without going to the load), and it's hard to imagine a real battery being wired in this way. For example, this never reduces demand charges.

Expected behavior

Add appropriate warnings or errors (ssc and maybe the GUI) for this situation such that users know they might want to consider a different utility rate option, such as net billing.