[IMP] improve the way indentation is done in pivot table (addon web_graph)

Previously, it was done in a ugly way: added several spans with the class
.graph_indent.  Now, it simply sets the margin of the content.
[FIX] add $ to jquery variables (addon web_graph)

the rendering code of the pivot table didn't use $ in jquery variables,
this commit fixes that issue and slightly simplify their names.
[FIX] render the pivot table correctly (addon web_graph)

The code was bugged: it added a <tbody> tag around each rows instead of adding the rows to a single tbody.
[IMP] optimize the pivot table rendering when folding rows (addon web_graph)

don't redraw the full table when folding rows.  instead, it removes from the dom the corresponding rows.  This should give a big speed boost when folding rows on big tables.
[MERGE] merge from trunk
[IMP] optimizes pivot table rendering when expanding rows (addon web_graph)

This patch makes the graph widget only add the rows that were new instead
of redrawing the full table when expanding
[MERGE] improve pivot table rendering

* don't redraw the full table when folding/expanding rows: simply removing/inserting
the rows from/into the DOM is faster
* add a $ in front of jquery variables
* improve the way indentation in row headers is done (was done by generating useless spans)
* fix a stupid bug: a tbody tag was added around each row of the table
[IMP] Add $.fn.button to jquery.ui noconflict template