Activation code lookup should be configurable

[tamw-wnet]

Noted that there was a hard-coded link to a page that depends on a separate custom WNET-specific plugin to do member activation code lookups on the userinfo.php template. I've added conditionality so that link and text go to PBS's member lookup tool if the WNET-specific plugin isn't there, in commits 2cdef79 and 46d20f1 . However, the member lookup link should be configurable, in a plugin setting.

[tamw-wnet]

noting that the change to make this happen would involve adding a couple of settings in class-pbs-passport-authenticate-settings.php around line 73, and then looking for those settings in templates/userinfo.php

[tamw-wnet]

@bymoulton credit for pointing this out