#1177 Added possibilities for import positions

[davidlamhauge]

"Tredje gang er lykkens gang" (Danish proverb)
I've made this extension to the much discussed import feature.
Here you can import relative to four positions, as shown in the screenshot below.
Whether my naming for the four possibilities are precise enough is up to you. Let's discuss it.

When importing to follow camera, we have to set the viewManagers importView for each image, which called for 4 lines of code in the Editor::importImage() function. If any of you know a smarter way, please tell me how.
Finally, this only addresses the urgent problem of the merged feature, that could be more precise. We should have a feature where we could import to whatever position we want. That must be another time.

[MrStevns]

LGTM.

It could be considered whether we should have an ImportManager now, since that functionality is growing in complexity, I also think it's unnecessary to look up the layer for every image is imported, since we know it's always the same.

It's not crucial right now, hence my approval but I think it should be done sooner rather than later.