Add a way to distribute/straighten linked blocks

[cromo]

Until #2 is completed, there will be no way to move multiple blocks at once; the user must move each block individually if they want to place a chunk of code in a different location. Furthermore, there's no easy way to align blocks to make them look nice and improve readability. This issue proposes a mechanism by which a user can automatically lay out a series of blocks for optimum readability which has the side effect of allowing the user to move multiple blocks at once.

The proposed inputs are to grab either end of some linked blocks in each hand and press some button combination to trigger the distribute mode. Upon doing this, all blocks between the hands will evenly distribute themselves between the blocks in the hands and will continuously be redistributed until both hands let go of the boundary blocks. (This allows the user to place one as an anchor while still holding on to the other to lay them out more precisely or over longer distances.)

To begin with, this may be a linear placement of block center points weighted by the width of their text contents, but a nicer distribution could be done by spacing the blocks out on the arc created by the position and rotation of the held blocks.