Home page box

[ajparsons]

Related to #1789 and #1791

This is a go at reducing some of the elements on the home page - as the search box now accepts postcodes, we can combine the two search boxes together. This PR:

• Applies some of the colour changes lucas suggested - but sidesteps the big homepage colour problem by getting rid of it.
• Creates an abstract search box that's customised for each Parliament
• Different images are used for each Parliament (some need to be licensed or changed before deploy)
• Adds a few quick links - which will also take the 'your mp' link when the cookie is set.

If we're broadly good with this approach, need to:

• Adjusted tests to look for new content
• Create a new 'about' box below that brings the 'who we are' onto the homepage.

Known issues:

• Not loading different sized images for mobile, etc

[ajparsons]

I think this is hitting the point where it needs a designer to have a think - @lucascumsille ?