[test] map pgettext to unicode as _

[table view] fix bug introduced in 7938:80c6e2155c3d leading to not translated table headers

oops

[test] fix some failures recently introduced

add missing imports

[selectors] match_kwargs and match_form_params selectors both accept a new `once_is_enough` argument (closes #1990438) also fix docstring of match_exception and references to selectors in the book.

[cache] replace lgc.cache with something more appropriate (closes #1921713)

merge and fix cubicwebSortValueExtraction pb which disappeared when tablesorter.js has been updated

[table] use explicit add_onload() to setup table sorting (closes #2013493)

[schema display] display_name shouldn't call .lower(). Note the only proper way is to have different msgid for upper/lower cases. Closes #1105433

[ms repository] when an exception is raised during extid2eid and no rollback is done, some manual cleanups have to be done (closes #1993420)

[facets] on the way to vidargs removal our roving on the table view, which leads to introduction of this feature, proved it was not the way to go.

[migraction] fix cmd_change_attribute_type command (closes #2015073) use dbhelper to avoid issuing unsupported SQL

[action] has_editable_relation first argument is once_is_enough flag, not an action name

[table] Only apply sorting event on the first row of a table header (closes #1988780) We use the new selectorHeaders from table-sorter 2.0.5

[table js] Update jquery-tablesorter to 2.0.5 (closes #1989018) The cubicweb specific code is moved to the table view. This version add a new useful option for #1988780