delete attachment. PMT #95516

Decided for now to *not* try deleting the actual file off S3. I
think once we start doing that, it gets us into needing to have
a story on how those assets get archived, etc.
only capture the few WIND/CAS affiliations that we care about

DMT is internal, so there's no reason to map course affiliations to Django Groups.
pull in a very simple whitelist mapper (https://github.com/ccnmtl/whitelistaffilmapper)
and configure it to only map users into the couple groups that we might
even remotely care about.
add user to group. PMT #95446
include INPROGRESS items in estimate reports

for Graphite purposes, items that are INPROGRESS should probably get
counted in the same category as OPEN items. ie, red on the graphs.
Merge pull request #76 from thraxil/delete-attachment

delete attachment. PMT #95516
Merge pull request #77 from thraxil/no-class-affils

only capture the few WIND/CAS affiliations that we care about
Merge pull request #78 from thraxil/add-user-to-group

add user to group. PMT #95446
Merge pull request #79 from thraxil/include-inprogress-in-stats

include INPROGRESS items in estimate reports
introduce PrevNextWeekMixin
add WeeklySummaryReportCalculator
wip