new logging config logs the whole DDR stack; suppress celery status

After much wrangling, configured Django to log messages to a file.
LOGGING['loggers'] don't seem to want to write to FileHandler,
while LOGGING['root'] works.

Log files are rotated daily, kept for 2 weeks.
Notices for Celery status requests are filtered out (these were
being sent every 3 seconds).
logger = logging.getLogger(__name__)
request.META['RAW_URI'] is not always present, use something else
added @ddrview decorator for clearly marking views in logs

View start is clearly marked and useful basic metadata is pritned.
- HTTP method
- URI, query
- HTTP user agent
- view function and args

@ddrview decorator added to certain views:
- user login/out
- content creation/edit
- sync
- git status
slightly better logging of storage issues, mount/unmount
added logging entries for collection/entity creation errors
Resolved merge conflict in ddrlocal/dddrlocal/models/files.py