Added SecSign ID JS Api

The SecSign ID JS Api is used to automatically login a user after the
access pass was accepted. The automatic login is for both, the admin
panel and the normal wordpress site.
Added SecSign ID JS Api
Added checks for missing parameters

Added checks for missing parameters which could cause php errors
otherwise.
Automatic login, fix for wp multisites

The user is automatically logged in.
Fix for multisites: login on one site was working on all sites in this
multisite
Fixed redirect url problem, hidding password login on interim login
Corrected messages and texts.