Allow better choice of viewers

[tdudgeon]

The links to input and output files in job execution results (and maybe other places) always seem to use the plain text viewer.
e.g. the link takes you straight to the plain text view even though the browser view might be more appropriate.
For files in the project view you get taken to an intermediate page which lists the different types of viewer. This is more flexible but a little cumbersome as you need to click again on the intermediate page to choose your viewer.

As an interim solution it would better to always go to the intermediate page (which could also display more info about the files mime/type.

A better longer term solution might be that the clicking the first link shows a popup of the available viewers, letting you go directly, or go to the intermediate page for more info.

Also, we should aim to allow the types of viewers for a file type to be configured using the types endpoint, which contains info like this:

    {
      "file_extensions": [
        ".csv",
        ".csv.gz"
      ],
      "mime": "text/csv"
    },
    {
      "file_extensions": [
        ".tab",
        ".tab.gz"
      ],
      "mime": "text/tab-separated-values"
    },

That can be extended to allow additional viewer types and a preferred viewer to be defined. But until we have additional viewer types this is overkill.