Small changes for fixes to (#3014) and (#3019) - exception handling for when curl is missing being the main one

Not sure quite how I missed this before.

It now is ordered a bit more sensibly. Improved help and description
text on the page. Added a button to allow admins to delete users.
Improved the suspension/unsuspension process.

A public group is one for which many pages are open to the general public - not just site users, but also the public, and search engines.

It's now a %s based string, which means we can change the logic later and only have to update the lifetime in one place.

(cherry picked from commit 29dd5e39)

Largely, this is to clarify what this setting actually does, and why you would change it.

If a new institution is being created and registration is turned on, automatically insert an internal authinstance.

Cleaned up the message relating to this behaviour too. This change make it easier to add institutions.

Hide institution authplugin dropdown for institutional admins; print warning when no auth plugin is configured

This at least gives admins the chance of doing this if they want to.

Improved the wording for the Upload CSV page, especially in the case of institutional admins. Fixes #2214.

Previously, Institutional Admins were given links to pages they couldn't edit.

Instead, generate a list of users who we could not send e-mail to, and display this to the uploaded, with more detailed reasons in the server error log.

* Force password change: if checked, users are forced to change their password on next log in. This was mandatory before, now people uploading CSV files can choose.
* E-mail users about accounts: if checked, users are sent an e-mail about their new account. This was never an option before and never happened, now it is on by default.

We send a slightly different e-mail based on whether the user needs to change their password or not. This affects the Add User script a tiny bit.