Add ticket section and replace speakers with sessions page (#121)

* Improve styles for mobile users and update link to sessionize API

* Properly ignore generated files

* Add ticket section

* Add tickets link to the menu

* Do not link to the sessionize app yet.

Add a nice sessions view instead of the speakers view

Add a more intersting tickets section

Remove the contact us link form the call for sponsors section since the link is also in the text

Refactor speaker popovers to be usable everywhere and animate them.

* Load images of the hero eagerly

Author: andreas-taranetz