organisation: Add missing search setup for Projects
Replace all placeholders in apphook pages

Apphook templates should not contain {% placeholder ... %} tags, due to
their unusual ability to be rebound to different pages. They *can*
contain {% static_placeholder ... %} tags, and this commit replaces all
the placeholder tags in such pages with their static equivalents.

Note that static placeholders must have a globally unique name.

In addition, I've taken the opportunity to improve our string coverage
for I18N.