define window for showing a mussa alignment

define window for showing a mussa alignment
Create a new window to hold the mussa sequence alignment. (aka
show all the sequences lined up at a starting point with lines connecting
base pairs.)

(This also fixes a bug I introduced into the fltk version of mussa back
when I changed paths from just being a vector of ints into an actual
class.)

I still need to actually allow the user to pick the aligned path and show
the conserved base pairs.