[FRG] Improve band line visual positioning

[beauwest]

Right now, if you want to put a band line before a band, for example, in a footer, if you position the DOM elements to where you can see both of them, it ends up creating a lot of white-space.

Since bandLines are usually thin, you have to overlap the two in the visual editor to prevent whitespace, and that makes look weird and unclear when editing it later.

#234 would likely solve this as well.