MTC Enhancements 03/2020

[landonreed]

• Update feed version dropdown (reverse sort, retrieval method filtering)
• Add field length validation checks (per requirements set forth in 511 Transit_Data Guidelines_V2.0)
• Add ability to transform GTFS feeds, including:
  • Replace file (e.g., stop_attributes.txt) in new version with file from previous version)
  • Replace file in new version with user-defined CSV data

[binh-dam-ibigroup]

Closing this issue, the transformations were handled by #579, field length validation in #648.