Make it clearer what the rummager rake tasks do

It wasn't clear that these tasks index more than just "documents". In
fact they either index detailed guides, or everything else that is
searchable.
Rename misleading methods

At some point in the distant past, Whitehall.government_edition_classes
did actually return only Edition classes. Now, it returns all classes
that are searchable and should be indexed in the "government" index,
i.e. all searchable classes except DetailedGuide. I've renamed these
methods to avoid confusion in the future.
Start role year selects at this year, not 1700

* Starting from 1700 and having to scroll all the way down to 2014, or
even 2019, is painful
* Restrict date entries to current year rather than current year + 5
which seemed to be the default
Don't override passed in STATIC_DEV env var in startup.sh

Instead, conditionally set it to a default.
Merge pull request #1657 from alphagov/tweak-startup-script

Don't override passed in STATIC_DEV env var in startup.sh
Indicate that change notes are public

* Research showed that it wasn’t clear whether this note was internal,
like remarks are, or visible to the public
Confirm announcement is published

* The button action says “publish”, this should be affirmed in the
flash message
SupportingPagesController inherits base class

The SupportingPagesController doesn't need to be a special little
butterfly; it should inherit from DocumentsController like all the rest.
This fixes a bug where unpublishing was not working for supporting
pages.
Rename method for clarity
Refine role copy

* The second part of the sentence was hard to understand
Merge pull request #1656 from alphagov/rewrite-code-for-clarity

Rewrite code for clarity
Merge pull request #1658 from alphagov/improve-role-date-selection

Improve role date selection
Handle CSV preview issue

This improves the handling of badly encoded CSV files so it fails more
gracefully when encountering dodgy characters.
Mark non-public methods as private
Merge pull request #1655 from alphagov/csv-preview-robustness

Handle CSV preview issue
Merge pull request #1661 from alphagov/public-change-note

Tweak statistics announcement copy
Rename feature file to be more generic
Failing feature for cancelling stats announcement
Add model/interface for cancelling announcements

Inlining styles straight from fofr's mockups for now. Will rationalise
the CSS in a later commit.
Remove delete from stats announcements

Users should not be able to delete an announcement once it's been
created as we do not want to lose the permenant record of an
announcement. Instead, announcements that are no longer valid should be
cancelled.