atof() on Windows expects "," (comma) as float delimeter and ignores "." (dot). So on windows atof("0.1") would return 0.
Unlike MAC.
Proposed fix should work on all platforms.
This makes continued merges with ardour codebase easier, at the
small cost of removing the XML-based constructors. They were not
in use anyway and their use doesn't really fit into the
conception of the canvas as a dynamic UI element. Could reintroduce
them at a later date.
