This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
BUGFIX: navigation bar should always activate the right tab (even when diging into a top period)
BUGFIX: /top pages titles
BUGFIX: no "edit category" button on /top page after visiting a category
BUGFIX: properly hide category columns when there is no children category (on both filter + top pages)
BUGFIX: promises not caught when scrolling down a topic list to load more of them
BUGFIX: CSS on category dropdowns
Updated `top_menu` i18n with available filters
