644 mobile app links

See #644 -- would like this to go live promptly please to assist the commercial team.

Note I *felt* like I might be breaking somethig in phonegap's code here, because some of the `footer-mobileapps` casses were being used there… but this I believe is just remnant code that hasn't been tidied up, and actually that's all neatly separated in the `fixmystreet-mobile` repo.

Could somebody check this is sound please?