Incentives page should provide warning about PBI and grid charging

[brtietz]

Describe the bug

#1542 Provided a warning to users who attempt to use the PTC with grid charging. The same warning should apply to PBI.

Expected behavior

Add a warning to the incentives page if the user specifies PBI with a grid charging battery.

Tagging for patch 2 to be ambitious, but realistically it's fine if this slips to the release.