New pivot view

new pivot view, full rewrite of graph view

This branch is a split of the former graphview into a pivot view (the
tabular view) and graph view (the various charts).  The code was fully
rewritten.
* pivot view should be faster (better underlying data structure and
better algorithm)
* better integration with the web client (use of sidebar, of menu buttons,
bettor style)
* new feature: pivot view can be sorted
* new feature: pivot view cells can be clicked to open a list view with
the corresponding domain
* web_graph addon was removed, and the graph view code has been moved
to the addon web.
* the interaction with the searchbar was changed (no more column facet)
* better and simpler code for graph view
* mary corner cases in graph charts have been corrected (for ex, pie
chart with positive and negative numbers)
* graph/pivot correctly save their state when added to dashboard/saved
(state such as current measure, chart mode, column groupbys, ...)