Add metadata to the venue page

[nuest]

Depends on #79 and may better be split up into multiple issues when started.

The venue landing page should show some minimal metadata about the venue. Currently, the page only lists the checks:

https://codecheck.org.uk/register/venues/conference/AGILEGIS/

It should also provide the following information:

• contact email regarding CODECHECK
• URL
• logo via an external logo URL (we don't host the logos)
• short description
• identifier(s), such as ISSN, ROR, event identifiers (ConfIDent), ...

The final page cold look something like this:

The information should be stored in plain text files in the register, e.g. in a folder collections with YML files, such as gigascience.yml:

contact:
    name: Edd Editor
    email: edd@giga.science
url: https://giga.science
logo-url: https://giga.science/logo.png
identifiers:
    - name: ROR
      value: bla
      link: http://ror.org/bla
    - name: ISSN
      value: 1234-5678
      link: https://issn.org/1234-5678
description: |
    The journal is...