Auto hide layers and save button in editor

[johnnyblasta]

Hides layer selector button when only one layer is editable.
Hides save button when autosave option is true.
Closes #1494

[steff-o]

Tested in Chrome on Windows. There is a wider gap between the save button and the button next to it if layer selector is hidden. Probably because the layer button is inside the popover-container. Hide that div instead removes the gap.

[johnnyblasta]

Tested in Chrome on Windows. There is a wider gap between the save button and the button next to it if layer selector is hidden. Probably because the layer button is inside the popover-container. Hide that div instead removes the gap.

Made a fix that hides popover-container instead which makes the extra wide gap disappears

[steff-o]

LGTM. Still there are some strange stuff going in in the editor toolbar, but that's not because this PR. The add feature button is also wrapped in a popover-div that separates it from the other buttons a bit and the editor layer popover contains a body tag. But both those have been there for ages.