The instancename field is an human-readable version of the institution
name, so can't be used for comparisons. authname is the
computer-readable one.

Prevents upgrade crash when there's no profile icons in the system.

This is so we don't store a value that we might be ignoring when
displaying the form again.

Still needs to be translated.

Send some more data when a site is registered - mainly grouping views by viewtype and artefacts by artefacttype.

Tidy up the registration form. Display the data to send in a table, add a "send weekly updates" button.

Give installs an installation key which we send back to mahara.org to prevent people sending bogus data for other peoples' wwwroots.

These constraints won't work on MySQL. Tough.