Add multiple fonts support

I would like to use different fonts for different languages characters (e.g.
English letter and Japanese kanji).

This pull request enables Light Table font-family setting to accept a string
or a vector of strings.

```clojure
{:+ {:editor [(:lt.objs.style/font-settings
               "Menlo"
               "10"
               "1.2")]}}
```

```clojure
{:+ {:editor [(:lt.objs.style/font-settings
               ["Menlo" "Hiragino Maru Gothic ProN"]
               "10"
               "1.2")]}}
```