#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 closes #49.

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? I've assigned it to @dpmatthews for the discussion.