add agent string to changelogs, git commits

Changes performed though the web UI will have agent "ddr-local".
Changes performed by import script will have agent
"importers.densho".
ensure agent string is passed through add_file task functions
accept lang fields with CODE:NAME in addition to just CODE

Many of the spreadsheets have langs formatted as
    eng:English;jpn:Japanese
and it's too much trouble to change them all.
added ddr-lint setup to update.sh script
made update script a little nicer-looking
mv guts of elasticsearch code to ddr-cmdln
Added italian as language choice in entity model.
Corrected list syntax error in entity.py
added python-dateutil to requirements
rm nginx default.conf on install,update
fixed sync bug: added missing elasticsearch host arg
Fixed sorting of entities in collection detail view.
fixed handling of entity creators field names,roles

Several variant data formats are present. This change converts
variants into the standard format:
creators: [ {'namepart':'NAME', 'role':'ROLE'} ]
add src/dest file sizes and paths to add_file logging
use the correct command to get annex status
use cached repository git status/git annex status in view
use jQuery to update collection git status after initial page load

Getting git status for every repo in the collections list page
takes a long time once collections get big.  Statuses are now
retrieved by jQuery after the page has finished loading.

Room for improvement: If we had a function that returned status
only on cache hits, we could load status into the view context
and only use jQuery for cache misses.
treat Entity.digitize_date as freetext rather than as a datetime

issue #145
first draft of twill tests
cache pip downloads