Appion

this is based on imcached logic with the following changes:

- uses imcacheconfig for redux settings
- uses generators instead of threads
- can query arbitrarily long ranges (imcached runs out of memory)
- can filter by session, user
- by defaults sets max-dt to 6m ago and deletes mrc after archive
- optionally delete mrc post facto (forward mode)
- can generate reports
- can deal with relative links (a linked to a-DW)
- safely (atomically) create mrc. no data corruption even if two imarchive are pointing at the same data source.