Editing an extension no longer drops User Manager group memberships

[vladm]

The extension page's 'User Manager Settings' hook treated a missing userman_group POST field as "remove the user from every group". Since a disabled multiselect (directory without modifyGroup permission) and a selection cleared by javascript both post nothing, saving an extension could silently strip the linked user's group memberships.

• Add a hidden userman_group_submitted marker, rendered and kept enabled/disabled in lock-step with the Groups field, and only sync group membership when it is posted; an absent field now means "no change" instead of "remove all"
• Consolidate the four duplicated sync/strip blocks into userman_sync_groups_from_post(), scoped to the directory whose groups were displayed, guarded by that directory's modifyGroup permission (previously the default directory's permission was checked)
• Disable the Groups field based on modifyGroup instead of modifyUser
• Fix usermanSetFields() strict indexOf comparison of numeric ids against string select values, which cleared the Groups selection whenever the Link to a Default User dropdown changed

[sangoma-oss-cla]

All committers have signed the CLA.