Terms of service and privacy policy feature.

If enabled, terms of service link will be shown in sign up page.

[Base for discussion on Loomio](https://www.loomio.org/d/ezlIV5rN/add-tos-and-pp-documents-for-podmins-to-use?proposal=k0LZg1M9#comment-128186).

So yeah, if enabled (default false), /terms route will work and contain either the basic template (default.haml) or custom written by podmin (terms.haml). Same templates are used for mobile too - we shouldn't duplicate these I think.

Also I'm sceptical whether there is need to allow somehow creating different language versions. Podmin can write it in whatever language they want or in different languages.

No tests yet, should probably write something for the setting <-> route functionality. Also is this as a feature something we want? Also the base template would need some discussion.

The terms are from [here](https://github.com/jaywink/terms-of-service) - though a little modified in this pull. I'm going to just delete that old repo. I've taken a print out from my local dev box for a little more convenient viewing :) [Check it out here](https://cloud.jasonrobinson.me/public.php?service=files&t=5e0e94be26f0a11b4a810d2bc72c5993).
I'm not completely sure what to do here. Whatever we call it, it's still a document outlining the rules for using the website. I'm not sure calling it something else will change that. Calling it ToS will not make it any more or less legal (AFAIK) than calling it 'rules' or something - but of course not a legal expert.

Other comments have been implemented in latest commit - will squash once finished.