Record a log of datafeed source imports (closes #2026097) Formatting, css and js stolen from narval.

[management table] upgrade sources groups management table to new api

[management table] fix and upgrade users and groups management tables to new api

[table views] closes #1986413: refactor TableView, EntityAttributesTableView, PyValTableView See the tickets for a description of the why. * one should now use RsetTableView instead of TableView and EntityTableView instead of EntityAttributesTableView. * a flexible layout object has been extracted, TableLayout * PyVaTableView has been rewritten using the same base class / renderer

[web component architecture] extract LayoutableMixIn from components in the intend to use it in the table refactoring to come.

[diet] drop pre 3.6 API compatibility (but attempt to keep data cmopatibility). Closes #2017916 notice drop of the .paginable property necessary for 'paginable' affectation as done in the forthcoming table views refactoring

[test] restore support for python < 2.6

[forms] update code broken by linkto refactoring

[rdf] drop buggy (name error) try/except (done using related(safe=True))

backport stable