Reword CTA copy on frontpage banner

In user testing no one clicked "Start Now" to make a request. All users clicked
"Make a Request" in the main nav, so lets try that here.
Add cache-busting to request response notification

Users get a new response email, click the link, but get a cached page.
This is a quick fix to ensure they always see the response when clicking
the link.
Use new status icon names (with old icons)

Defining the basic css for status icons here so that themes can just set
colours and add their own icons.
Remove FasterCSV dependency

The last remaining usage was removed in c1ee22fe
Example blog now runs over https
Merge branch 'rails-3-develop' of ssh://git.mysociety.org/data/git/public/alaveteli into rails-3-develop
Merge branch 'feature/responsive-icon-css' into rails-3-develop
Merge branch 'issues/1496-main-banner-cta-copy' into rails-3-develop
Remove duplication from new correspondence urls
Move date helpers to DateTimeHelper
Add specs for DateTimeHelper#year_from_date
Add specs for DateTimeHelper#simple_time
Minor tidying of DateTimeHelper and specs
Remove DateTimeHelper#year_from_date

DateTime, Date and Time all have #year methods
Extract public body CSV export to its own class

- SRP: Do one thing. PublicBodyCSV converts a
  collection of bodies in to a CSV formatted
  String
- Adds some parenthesis around parameters in
  PublicBodyController#list_all_csv
- Let the controller handle what records to pull
  out for the CSV export

Arguably this doesn't really need to be anything
to do with PublicBody, but it allows us to set
nice defaults.
Add PublicBodyController#list_all_csv specs

- Shouldn't include non-visible bodies
- Shouldn't include internal admin bodies
Move PublicBody domain logic from controller

Moves the magic 'site_administration' tag logic to the PublicBody
model. Easier to make the string passed to `PublicBody#has_tag?` configurable
if we want to allow this to be set per install.
Allow a message with more than one event to be destroyed.

Fixes #1569
Handle converting empty RTF files

Fixes https://github.com/mysociety/alaveteli/issues/1563
Merge branch 'hotfix/0.18.0.2'