fix wrong calculation of clean_session_interval

[ITree] more fixes, fix fixes

[idownloadable] depends on a new mtconverter release

[ITree] fix adapter/_done_init to handle tree_[attribute|relation], add maxlevel argument to base tree view since one side effect of the new code is that it find tree view for entity types it didn't find before, hence one may want to limit tree view depth when it wasn't necessary before

[3.9] fix tests

[web] move itree adapter to entities, it may be used outside the web interface

[view] add a new entity_call method to entity view protocol, allowing some to work with not yet created entities. Also, start considering 'eid' form parameters where we only consider 'rql', so we can move on bloquing arbitrary rql inputs (more to do on this...)

[idownloadable] refactor IDownloadable primary view to make overriding easier

[web] ajax_replace_url superseed build_ajax_replace_url, more generic and relying on the json controller (closes #750090)

[form] refactor meta-attributes handling: hide them by default using uicfg.afs instead of returning None (or not, according to skip_meta_attr flag argument) in guess_field

[repo] fix typo

[req] fix format_time w/ 0:0 which is evaluated to False