Make the 3rd zoom button always zoom to extent

[olliethomas]

I made a mistake in describing the functionality of this button. This is now the new functionality of this button.

Given I have an extent marked

When I click the zoom-to-fit button

Then the map zooms to fit the extent, ignoring other layers outside of the extent.

[olliethomas]

Maybe this shouldn't be the function of the 3rd zoom button, but could instead be done when clicking somewhere else e.g. the zoom level indicator?

Currently the 3rd zoom button fits all non-base layer layers to the map

[paulthatjazz]

Just a thought, perhaps we could remove the 3rd zoom button and add zoom to layer buttons elsewhere?