Clean up loader_common
Clean up loader_common

- name iframe/doc variables according to meaning, not type
 - don't unnecessarily pass around config by json-ing and then decoding
again.

daukantas/factlink-core,Factlink/factlink-core,daukantas/factlink-core,daukantas/factlink-core,Factlink/factlink-core,Factlink/factlink-core,Factlink/factlink-core,daukantas/factlink-core