Styling the plot tooltip

**Issue by [chaorace](https://github.com/chaorace)**
_Tuesday Feb 21, 2017 at 23:50 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/313_

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Despite having cleaned up the plot tooltips already, they're still a bit of an eyefull. I think this tooltip could benefit greatly from some selective italics and coloring. For example: color-coding strategic/luxury resources so they're easier to tell apart at a glance and to spot in the middle of all that info.

The descriptive text could also use some styling to make it easier to distinguish the demarcation point between the labels and info. e.g: Movement Cost: 2 -> _Movement Cost:_ 2

[See here for more info](https://forums.civfanatics.com/threads/cqui-a-qui-spinoff-v0-6-out.602771/page-21#post-14660182)

Start by locating the Lua implementation of the plot tooltip UI and review the linked forum example for the intended presentation. Update the tooltip styling so strategic and luxury resources are visually distinguishable and descriptive labels are separated from their values with emphasis. Done means the requested styling is visible in plot tooltips without obscuring the information.

Written by the indexing model from the issue text.