Add option to set alignment when multiple blocks were selected

[phpbits]

It'll be really great to atleast have alignment option when there are multiple block selection.

[lubieowoce]

thought i'd let you know – i figured out how to do something like this, and have a working prototype. here's a gif:

other core formats work too (made the gif before i implemented that), but it's pretty hacky rn - tricking the editor into showing those RichText format controls and applying the edits to multiple blocks at once isn't easy :/

i'll be posting updates on this gutenberg issue if you're interested!