FileMailer 0.1.0 beta 3

This beta fixes Google sign-in in the distributed application.

• FileMailer now uses the public native OAuth redirect flow. No Google client secret is embedded in the application or the source code.
• The application and Finder extension are signed with Developer ID.
• The application and DMG were accepted by Apple notarization, and both tickets are stapled.
• SHA-256 checksums and the SPDX dependency file are included.

While the Google OAuth project remains in testing, only Gmail accounts added as test users can complete sign-in.