1.0 device caching

Even though it will probably outdate soon, this change trades minimal RAM usage ( there should not be so many different browsers around )  for speed.
Profiler said, about 20% runtime is saved.

time misc/log-analytics/import_logs.py  --token-auth=1a***c3 --url=http://piwik.local --idsite=2 --hostname=* --strip-query-string  --recorders=16  --recorder-max-payload-size=2000 --debug /tmp/SSX_T150K  ### 150K Lines

Performance summary 1st run Caching:
     Total time: 44 seconds
     Requests imported per second: 953.63 requests per second

Performance summary 1st run 1.0:
     Total time: 62 seconds
     Requests imported per second: 688.04 requests per second

Performance summary 2nd run 1.0:
     Total time: 61 seconds
     Requests imported per second: 693.58 requests per second

Performance summary 2nd run Caching:
     Total time: 46 seconds
      Requests imported per second: 920.71 requests per second