Resizeable Sidebar/Views

[NXXR]

Make the sidebar (or all segments) resizeable by providing a handle to move the separators perpendicular to their border. Also change the cursor to col-resiz/row-resize on hover to indicate possibility to resize.

Maybe add a toggle to enter layout changing mode and hide the separators otherwise? Alternatively, just change cursor to indicate that the separator can be dragged when hovering over the separator.

Waiting on:

• #38