Add a view menu item for the unit controls bar

[jwrober]

Is your feature request related to a problem? Please describe.
Not all players want the unit controls bar to be present and it can get in the with the city screen on smaller resolution displays

Describe the solution you'd like
Add a view menu option to toggle the display of the controls bar. Might also add an x close item to the bar so it can be closed with with quick click.

Describe alternatives you've considered
There have been other discussions of pushing the buttons/features of the unit controls bar to the lower left corner, see #750

Additional context
Still many complaints about the city dialog interfering with other things on screen. Hence #1591