admin:statistics_announcements/index handles nil org

Users without an organisation viewing the statistics announcement index page
should not raise an exception.
Remove duplicate method implementation that exists on inherited class

Found this method while trying to understand how uploads work. It
looks like it's a clear duplicate of the same code that exists in the
`Row::attachments_from_columns` implementation[1].

[1] https://github.com/alphagov/whitehall/blob/7db851b66dcc6a144443ee281c5c03ae32d54253/lib/whitehall/uploader/row.rb#L136-141
Remove faulty data migration

This migration runs only on one machine in
production hence doesn't clear cache from
all nodes.
Set default expiry time for taggable helper cache

it is good to have an auto-expiration time on these
cached values otherwise they only get refreshed when
the memcached runs out of space and clears them or
the machine restarts.
Merge pull request #1803 from alphagov/set-default-expiry-time

Set default expiry time for taggable helper cache
Merge pull request #1801 from alphagov/remove-duplicate-attachments_from_columns-implementation

Remove duplicate method implementation that exists on inherited class
Merge pull request #1802 from alphagov/fix-data-migration-to-clear-cache

Remove faulty data migration
Merge pull request #1798 from alphagov/exception-watch-users-without-organisations

admin:statistics_announcements/index handles nil org
Fix ODF highlighting include ODS

ODF is the format group, ODS is the spreadsheet format, which was missing
Merge pull request #1804 from alphagov/fix-odf-extension

Fix ODF highlighting include ODS
Fix GillSans font stack

* On IE neither GillSans nor Gill Sans were matching
* In Chrome on windows, Chrome has been known to pick “Gill Sans Ultra
Bold” instead

Applying fix from admin template:
https://github.com/alphagov/govuk_admin_template/pull/41
Merge pull request #1805 from alphagov/fix-gill-sans

Fix GillSans font stack