DAS new feature: Keyword search

proposed changes to config file:
* config.web_server.adjust_input - need to be disabled as keyword search give better suggestions
* keyword search has these two important options:
  * config.keyword_search.kws_on - is keyword search enabled? if set to True, keyword search results will be loaded through ajax. it can be processed locally or from a remote host if config.load_balance.kws_host is set.
  * config.keyword_search.kws_service_on - enables keyword search service on current host (slightly computationally expensive). 

proposed plan in case of performance problems in production (as discussed with Diego):
  * because this function is good to have, but is not vital one, we will point keyword search to a CERN virtual machine (this is loaded from client's browser so do not impair security of other services).  still better than to lose the functionally completely, and better than to impair performance of other core services
  * set config.keyword_search.kws_service_on=False
  * set config.load_balance.kws_host='das-kws.cern.ch' (point to a virtual machine)