correct membership tense

Handle cases when we have a start and an end date to prevent things like
current memberships using 'will be a member of'

Fixes #663
add alternative image URL to match API schema

The API uses a different URL scheme to identify images so add an
alternative one for the UI so the two can match up.

Also update shrinkwrap to point at the version of the API that uses the
same URLs

For mysociety/popit-api#84
Pretty print json in production

This makes it easier to read in the browser when you don't have a json
prettifier extension installed.
Add a link to users PopIt instances
Update popit-api
Use the html url in search results
Use a middleware function for middleware config

Rather than exporting an object which then has to be added to app.locals
manually we simply export the middleware config as another piece of
middlware, which can then augments app.locals itself.

This has the added benefit of being able to do further configuration
beyond template locals if necessary.

I've also taken this opportunity to remove the dependency on the
'version' module, which was only being used here.
Move duplicated locals into config middleware
Move template config into a separate module

This configuration is duplicated between the hosting and instance apps,
so it makes sense to move it all into one place.
Make route middleware an actual piece of middleware
Only show copy API endpoint button if Flash is working

If flash isn't present/working then clicking on the button silently
fails so hide the button by default and only show it if flash is
available.

Fixes #622