Implement management of multiple viewports

[Guite]

It would be nice if there was a possibility for direct specification of different viewports.

At the moment all widget sizes and offsets are implemented for md. For example col-md-4 offset-md-2. This could be expanded to allow different settings for the other ones.

For example we could include shoelace.

• http://www.shoelace.io/
• https://github.com/erikflowers/shoelace-io

Layout data needs to store multiple values for each viewport of an element then. Also $contentItem->getMinimumAmountOfGridColumns() needs to return an array with elements for each viewport as well.

[rallek]

Before looking for a perfect final solution I am making a temporary proposal.

Part 1:

The plugins in setting do get a defaut setting for the different view ports ( a new column for settimngs will be needed). So you can set xs, sm, md, lg and xl. E.g. for breadcrumb you are setting all of them to 12. That means if you place a new breadcrumb into your page it will be placed full width (because md is 12). If you afterwards correct it with the mouse the new size will be used. If nothing is set in the plugin list all viewports will use the same setting like today.

Part 2:

After you have placed a new element on your site you can edit via the small arrow on the top right of the element the individual setting and overwrite the view port settings (but not the md because it is given already by the layout).

Part 3:

Add somewhere in the edit template a preview button for each viewport and open a modal with the right viewport width.. Might be it is wise only to show available viewports. It makes no sense to start a preview in lg on a smartphone I guess.