Sets up paper_trail tracking in important models
and add conference_id to versions for storing conference_id
of conference related objects as metadata.This will help in querying
for versions related to conferences.
Fix issues with factories & event types initialization.Import paper_trail testing helpers
Fix bug: Creating an event creates a useless version with event update
Add revert and view changes features to revision history
Places logo on a white background if image is smaller than the given
constrains.
Resizes the logo if image is larger than constrains.
Validation of presence of logo was moved cause file field wasn't getting
marked as required field ('*' thingy) in form.
`- if logo presence` was removed cause logo is mandatory field.
