[FIX] E-mail user indexing - add to conference

 * If user was registered in a conference before having an account (same e-mail), his/her identity will be automatically tied to the registration in question;
[FIX] SSO allow public external accounts

- e.g. Google or Facebook
[FIX] Backporting fix from master to v1.1
[IMP] Create indico.wsgi symlink in htdocs
[MIN] Update legacy blueprint
[DEL] Remove legacy mod_python files
[MIN] Remove dead UH classes
[MIN] Trailing newline in wsgi file
[IMP] Added Pagedown Editor and Previewer to abstract submission
[IMP] Added Markdown and MathJax integration to abstract submission, editing and viewing
[IMP] Pagedown and MathJax in external modules

 * Also included proper assets in headers
[IMP] Better looking preview
[FIX] Added the remaining Markdown editing and rendering in abstracts and contributions, cleaned some code
[IMP] First work on LaTeX PDF generation, not finished and still buggy
[IMP] LaTeX PDF generation on Abstracts and Contributions
[IMP] LaTeX PDF generation on User Abstracts Book
[IMP] LaTeX PDF generation on Contributions Book (on event page) and Abstracts compilation (in event management area)
[IMP] LaTeX PDF generation on Contributions compilation (in event management area)
[IMP] Added class to handle the all the PDF generation from LaTeX, organized LaTeX templates in specific files, some code cleaning
[MIN] Minor fixes in LatexRunner() and templates