Add shortcut for moving tabs within window, with similar control scheme as browsers

[theboymeister]

I've always liked to work with TONS of tabs, and didn't have a problem identifying them with CTRL+K.
But when I want to focus in on a few tabs for quick referencing/comparison between them; collecting them into a single 'clump' at the end and CTRL+pgUp/pgDn-ing between them is usually my preferred workflow.

My suggestion is to also enable moving the tabs with CTRL+SHIFT+pgUp/pgDn, or at least a command for it.

I'm grateful that we even have the option for it through mouseclick and drags, but when I'm working with close to a hundred tabs, I could accidentally move it outside my bar and make it a new window by mistake.

Seeing as my workflow with SumatraPDF has been almost 90% keyboard based at this point, might as well make it a 91% (and with 100% less mouse-click based mistakes).