Layout and Alignment methods for Sequences

[mfansler]

Some methods like leftAlign(graphics: Graphic*): Graphic or spaceHorizontally(margin: Double, graphics: Graphic*) could be super useful.

I've been doing rows and columns using foldleft and, like when dealing with the withName result, you have to add an arbitrary Phantom object. Having such methods could sweep that boilerplate stuff under the rug.