Allow the 'linear' convert type to work with colors and integers, like the 'timed...

Allow the 'linear' convert type to work with colors and integers, like the 'timed swap' one does.  Change the initial values when converting to 'linear' such that the 'rate' is zero and the 'offset' is the previous value of the parameter being converted.  Also did some general tidying up.

git-svn-id: http://svn.voria.com/code@617 1f10aa63-cdf2-0310-b900-c93c546f37ac