Add new panel for fullscreen minimap viewing

**Issue by [chaorace](https://github.com/chaorace)**
_Monday Jan 09, 2017 at 08:23 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/231_

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Similar to how the tree views are now, but with a very large minimap in it! I don't anticipate this being too difficult, but the minimap _is_ weird. The button for this view would probably be most at home on the button panel attached to the minimap

[More info](https://www.reddit.com/r/civ/comments/5mqlkl/long_feedback_on_civ6_from_a_longtime_series_fan/)

No files or tests are named. Start by reading the existing tree views and the minimap button panel mentioned in the issue; the proposed work would be complete when that panel opens a fullscreen minimap view.

Written by the indexing model from the issue text.