[MERGE] merge from trunk
[IMP] modifies the web client to be able to use the new 'lazy' parameter of the method readgroup (so now the client can requires a readgroup to be eager/lazy) (addon web)
[IMP] complete rewrite of the data loading code in the graph view, using the lazy/eager feature of readgroup.  The code is simpler and more efficient: it only performs a fixed number of requests (well, the number is 'fixed' in the sense that it does not depend of the size of the data being displayed, but it still depends on the number of dimensions) (addon web_graph)
[MERGE] merge from trunk
[FIX] correctly filters out empty groups in read_group results in the data loading code of graph view (addon web_graph)
[FIX] correct the expand functionality to avoid creating rows/cols in the other dimension of an unfolding action (addon web_graph)
[FIX] makes sure the internal data structure of pivot table is correct after update_data (the children were not correct when the tree of headers was not full, after an expand for example (addon web_graph)
[FIX] read_group has been changed to return the results with field:interval as key (for example, date_deadline:week), to avoid name collisions.  This commit changes the web client to make sure it properly processes the new result format.  No change at all for queries that do not use the field:interval format (addon web)
[MERGE] merge from trunk
[FIX] add missing semicolons, add a missing 'var' statement and remove trailing whitespace (addon web_graph)
[MERGE] merge from trunk
[MERGE] merge from trunk
[MERGE] this branch rewrite the data loading code from graph view to use the new 'eager' feature of read_group. 

It should improve the graph view performance in a big way (very low number of read_group requests, and that number does not depend on the amount of data)