Layers tool should have options to control what appears in header

[qqnluaq]

If a map uses only 1 or 2 layers, the UI widgets in the header of the layers tool are probably superfluous.
The global visibility control is just confusing if there are a small number of layers.
The filter is only useful with a large number of layers.
It might be desirable to have the legend toggle hidden, and legends always visible.

Propose to add configuration to layers tool to control all of these widgets.