Make row titles configurable via plugin API

[texodus]

Row titles for plugins are now part of the plugin API, via the names property of the initial config entry.

Example from D3FC:

ohlc.plugin = {
    type: "d3_ohlc",
    name: "[d3fc] OHLC Chart",
    max_size: 25000,
    initial: {
        type: "number",
        count: 4,
        names: ["Open", "Close", "High", "Low"]
    }
};

[texodus]

@matt-hooper @DevAndyLee I modified the D3FC plugin to use this new API, and removed the perspective-view.less file you had to inject in the <perspective-viewer> shadow dom. Let me know if these changes look good to y'all!

[andy-lee-eng]

This looks good to me 👍

[matt-hooper]

No issue from me.
Thanks