Add journals

[joeroe]

Adds seven diamond open access journals and some basic layouts for displaying them on the home page. Each journal has a file in _journals/. In terms of metadata I added an initial set of frontmatter parameters that seemed relevant:

• title: Title of the journal
• model: Open access model (e.g. diamond, gold)
• peer_reviewed: true/false
• url: Journal home page
• issn: (e)ISSN, which also links to DOAJ
• publisher
• languages: Languages accepted for publication (ISO codes)

We could of course add or subtract from this. Probably should also be documented somewhere.

Also some minor changes to the ruby packaging (added .ruby-version for rbenv users and tidied up the default Gemfile).

[bbartholdy]

Can we also add a topical tag? We could use this wiki as a starting point: https://en.wikipedia.org/wiki/Subfields_of_archaeology

[zackbatist]

Excellent! Thanks for getting the ball rolling on this :)

I agree we should have a tag to indicate the journal's topics and scope. I created an issue to discuss how we might go about it here: #2