#49: add titles/descriptions to gui hover-over

This change adds titles and descriptions for tasks and
families (if available) to the hover-over information in
cylc gui. There is now hover-over functionality in the text
or tree view.

This pull request is for discussion at the moment, not for merging.

The question is, is it evil to have titles for families via suite.rc settings like this:
```
[scheduling]
    [[dependencies]]
        graph = """
            FOO:succeed-all => bar
        """
[runtime]
    [[root]]
        command scripting = "sleep 100"
    [[FOO]]
        title = FOO, a long long way to foo                    # <- this bit
    [[foo1, foo2, foo3]]
        inherit = FOO
    [[bar]]
        title = bar, a name, I call myself
        description = """Triggered by FOO members.
        
These include foo1, foo2, and foo3."""
```

or are we OK with it?