Views engine

Hi!
Here's my first shot for the views engine we talked about a few weeks ago.

From commit f4afe35:
"The files contained in status/custom_*.py and status/templates/custom_* permit to have a views engine, i.e. a customised form in where you can choose the data you need from Livestatus datasources/columns, arrange them how you like (sorting, filtering, stats) and feed this data to pre-defined templates or your own ones. The views can be represented with simple dictionaries, and are therefore stored through the userdata module."

To rapidly test this, create your own views (link in the left menu) and pay with them, or use these predefined ones by adding this to your /etc/adagios/userdata/USER.json: http://fpaste.org/106649/01745996/ (there are 3 views, which use 3 different templates (table, openstreetmaps, and pie chart), so you'll have a good idea of what is doable with the engine).

This is a work in progress, but what is committed here is fully functional.
What I have on my roadmap (but let's go step-by-step):
* separate public and personal views, have a tool to better organise the left menu,
* have a dashboard which can use many views on a customisable grid,
* improve the UI, by adding the possibility to run commands on selected views, have a search input field, etc.

Let me know your thoughts!