Move Export button to secondary nav

[AntonKhorev]

Export is no longer a green outline button but rather a gray secondary navigation item.

The main reason for this is to allow Export to collapse into More. This lets the header to be narrower in compact mode. Hopefully then compact mode will be available above the Bootstrap medium breakpoint of 768px, which then can be made a fixed breakpoint for going between small and compact modes. (If not, maybe try moving the History button next.) See #4130.

I also don't hide the Edit button because it's easier not to hide it. If I kept it hidden exactly like it was before, the History button in the small mode menu would have had rounded borders only on one side. So coincidentally I also do here what #4839 tried to do except I don't need a vertical button group for edit-history-export. There's no Export in the group and Edit+History should fit horizontally.

[tordans]

This solution is a lot cleaner than my take at #4839

And in general I am all for re-evaluating the primary navigation, there is a lot of potential for some UX design and information architecture work here.

I am wondering if there is a way to keep this PR a bit closer to what we have right now:
In the desktop screen size, there is not issue with the export being part of the green button group.
Can we maybe keep the export part of the button group for the highest breakpoint. And only move it in the "more" navigation one breakpoint below?

On the dropdown menu screen size: Keeping the horizontal button group certainly is the cleaner solution given Bootstraps limitations. We will very likely need to revisit this once we add more mobile editors in the future. But we can look into that once we know the details.

[AntonKhorev]

I wanted to get rid of compact mode and move the secondary menu items in/out of More depending on how much space is available. It was easier to do it together with the fixed breakpoint for small mode. See #4862.

This is how it looks if you get down to the 768px breakpoint:

Seems to work fine, but that's in English. Here's Bulgarian, and now things don't fit even with fully collapsed secondary menu items:

Without the green Export button everything seems to fit fine:

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One of the alternatives to moving Export from buttons to the secondary menu is to move Export dynamically to More if there's not enough space. Traces, Diaries etc will move between the secondary menu and More, Export will move between buttons and More. That'll be a little more javascript.

But does Export deserve to be a button? Is it used often enough to justify this spot and then this moving behavior?

One advantage could be that if Export is moved to More and there's still not enough space, it's possible to similarly move History. But I don't know if there's a locale that requires this.

[AntonKhorev]

#2420 does the opposite thing and adds one more button.

[simonpoole]

There is not really a reason to keep the history button where it is: Assuming no revolutionary changes (aka multiple bounding box per changeset), the history function is not particularly useful and could easily be moved to create space for other things.

[AntonKhorev]

#3040 proposes to move export to the map toolbar instead