Define all omero.search.xxx properties in the Search sysadmin page

This commit should group all sysadmin content related to search into a single
page. Additionally, the omero.search.xx properties are defined as glossady
(i.e. indexed) and referred to using the `term` markup in the rest of the
documentation.

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Improve title of sysadmin search section

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)