Required exceptions are now handled in database migration. Updated alembic version

Changed exceptions. Updated alembic version
Database migration to support private bookmarks

Exisitng bookmarks should be public

Added specific exception

Updated SQLAlchemy requirements

Tests added for private bookmark support

Fixed lint errors

Fixed another lint error

Added all tests
Merge pull request #461 from sammyshj/databasemigration

Exisitng bookmarks should be public