change Control::{set,get}_float to Control::{set,get}_double and make almost all...

change Control::{set,get}_float to Control::{set,get}_double and make almost all Control-related stuff use double rather than random mixtures of float, double and some integer value ; make hans' program change stuff work quite a bit better (not finished yet) including keyboard edting of pgm change values

git-svn-id: svn://localhost/ardour2/branches/3.0@7514 d708f5d6-7413-0410-9779-e7cbd77b26cf