Import - Validation of Custom Field option values should be case-insensitive

During import, when we validate the incoming cell value to custom field multiple choice options - we should do a case-insensitive match (as we do for 'built-in enums like Gender, Individual Prefix, etc.).

To recreate problem, using our sample data import a row with GOTV Experience value set to 'SPEAKERS BUREAU' or 'phone banking'. These should match the stored values -but are being rejected due to case mis-match.