Sort out leftovers from the old fx module

Sort out leftovers from the old fx module

This commit is mostly to clean up the implementation of the initAnimation
method of the Fx Module (issue #547). It also fixes these issues: #552, #582
and #584.

Here is a list of the changes and fixes that are made:
* Add a plot and array method to SVG.TextPath (issue #582)

* Make the method plot a getter when no parameter is passed for SVG.Polyline,
SVG.Polygon, SVG.Line, SVG.Path (this idea come from issue #547)

* Allow SVG.PointArray to be passed flat array

* Change the regexp SVG.PointArray use to parse string to allow more
flexibility in the way spaces and commas can be used to separate points
(something like this is now accepted: '1, 2, 3, 4')

* Allow plot to be called with 4 parameters when animating an SVG.Line

* Fix a bug in the plain morphing part of SVG.MorphObj that is in the FX module

* Relative value for SVG.Number are now calculated in its morph method (idea
from issue #547)

* Clean up the implementation of the initAnimation method of the FX module
(issues #547, #552, #584)