[NF] Add config option IXP_FE_USER_HIDE_MOBILE

[listerr]

Longer description

If you use the contacts feature in IXP Manager, then mobile phone in users is a duplication of mobile phone in contacts. If enabled this config option IXP_FE_USER_HIDE_MOBILE hides the mobile phone input in the user edit page, instead we use only the mobile/phone numbers in contacts, so that users are not required to update it in both places.

LONAP doesn't have any users without an associated contact.

In addition to the above, I have:

• [ ] ensured all relevant template output is escaped to avoid XSS attached with <?= $t->ee( $data ) ?> or equivalent.
• [ ] ensured appropriate checks against user privilege / resources accessed
• [ ] API calls (particular for add/edit/delete/toggle) are not implemented with GET and use CSRF tokens to avoid CSRF attacks