[scanpix] create 4 instances of Scanpix search provider
[scanpix] create 4 instances of Scanpix search provider

The 4 instances are hardcoded as it is currently not possible to set
dynamically search providers in frontend.

fix SDNTB-217

ioanpocol/superdesk-ntb,ioanpocol/superdesk-ntb,ioanpocol/superdesk-ntb,petrjasek/superdesk-ntb,petrjasek/superdesk-ntb,petrjasek/superdesk-ntb,petrjasek/superdesk-ntb,superdesk/superdesk-ntb,superdesk/superdesk-ntb,superdesk/superdesk-ntb,superdesk/superdesk-ntb