Fix tests (delete whoosh dir when emptying DB)
Move debug flag to indico.conf
Refactor webassets usage

- Global core environment (not inside WPBase)
- Debug flag is checked in the constructor
- Jinja extension can be used
Add base jinja template
Don't try to connect to the db at import time!
Revert "[IMP] Consolidate big gaps in category statistics"

This reverts commit d51b103bc7ac90d9eb3d3944aaa307137f1fbbb0.
[IMP] Statistics page revamped
* First version
[FIX] Fixed a plot-related bug
* The values are now sorted and the plot is shown correctly
[FIX] # of users loaded into the BD
* Now the number of users is loaded into the DB by the statistics updater task
[FIX] Fixed axis rendering
* Now the y and x axis are rendered correctly
[FIX] Fixed x axis
* Fixed a minor error with x axis
* Added the "year" label
[IMP] Added jqplot plugins
* Plugins added: data point highlighting, mouse cursor tracking and plot zooming
[IMP] Several style enhancements
* Removed the grid from the plot
* Highlighted the current year data point
* Header adapts better to the page
* Added a button to switch to the category page
[IMP] JSON requests for statistics page
[FIX] Switched to AvatarHolder._getIdx
[IMP] Changed to smooth curve plots
[IMP] Admin creation wizard: first version
* Very first version of the admin creation wizard
* The interface is temporary
* Right now a new user with admin priviledges can be created
[IMP] Server's settings configuration
* Now the wizard will also configure the server's settings (instance tracking included)
[IMP] Confirmation page & tooltip
* Added a confirmation page after the wizard
* Added a tooltip for Instance Tracking in the Server Administration General Settings
[IMP] Expanding/collapsing sections