[FTR] Added simple eTicket PDF generation with QRCode

Introduced new dependencies: PIL and qrcode
[FTR] Added eTicket download link option after registration
[FIX] Add qrcode dependencie to setup.py
[MIN] Code style fix in TicketToPDF class
[FIX] Check for non-mandatory fields in PDF
[FTR] Add e-ticket tab to registration setup

- Add enable/disable e-ticket button to tab
[IMP] Use flasks url_for instead of urlHandlers

+ minimal code style fixes
[FTR] Add e-ticket link to registration page
[IMP] Add icon to e-ticket download link
[FTR] Add e-ticket tab to manage registrant view

- Add e-ticket download link to the tab
- Add info about the ckeck in status to the tab
[FTR] Add e-ticket download link to the menu

- Add migration to update the menu object in
  the database
[FTR] Add functionality to send e-tickets by mail

- Extend e-mail interface with attachment option
[MIN] Use dict instead of None as default attachemnt value
[MIN] Allow multiple attachments in emails
[MIN] Minimal code style fixes in etickets.py
[MIN] Use ctx manager to get user instead of session
[REF]actoring ETicket class and getModEticket method
[IMP] Use new function from util for date formatting
[FTR] Add CheckIn to registrants management
[FIX] Timezone issue with checkInDate