metadata view

[oliver-sanders]

Consider a view that displays metadata for a selected item.

Requires: #534
Complicated by: #434

If a task is selected in the tree view there would be a mechanism (e.g. double click/tap or drag&drop) to share that selection with other views e.g. this "metadata view".

The metadata view would just display all of the Cylc [meta] information present for the selected "thing" (i.e. task/family/workflow).

We could potentially support markup languages here (e.g. markdown, rst):

[meta]
    title = "My Workflow"
    description = """md
        **Hello** `world`!
    """
    URL = http://whatever.com

For example this metadata could be presented in a metadata view like so:

---

My Workflow

id: myworkflow//

Hello world!

http://whatever.com

---

Pull requests welcome!