Remove the filter action from the toolbar

I talked about this with both @ngraham and @broulik (separately) and there seems to be a consensus to not have it there. I hope you don't mind @meven.

This commit removes the "toggle_filter" action from the default toolbar configuration. It is not quite important enough to be always visible on the toolbar by default. Instead it is easily accessible through the hamburger menu and the menu bar.

The filter is only really necessary if one has a lot of items in the current location and one knows exactly how to identify a certain item among them by the name which probably isn't how most people browse their files.

There are also some more advanced use cases but advanced users will be able to either learn the keyboard shortcut or move this action back to the toolbar.