* Bug 15481 fixed: scatter() & scatter3d()

* Bug 15481 fixed: scatter() & scatter3d()

  http://bugzilla.scilab.org/15481

  Moved from master @ https://codereview.scilab.org/21373

  A short list of fixed issues:

  USAGES
  * scatter() nor scatter3d() could display a single data point (reported bug).
  * The type of X, Y, Z was not checked, leading to weird error messages.
  * X, Y (and Z) should have had the same shape, while only the same
    length is actually required.
  * The properties names were case-sensitive.
  * Colors could not be scaled to data < %eps.
  * Colors could not be specified by their #RRGGBB code nor their index.
  * The handle of polylines was returned even when not requested.
  * The example cleared the current figure instead of the current axes.

  INTERNAL
    a) Warnings were generated, instead of errors.
    b) Warnings messages were not standard.
    c) Warning messages were not localized.
    d) The same colorIndex name was used to name a function and
       a regular variable.

  DOCUMENTATION
    * The thickness option is for all markers. It was not indicated.
    * Examples:
      scatter():
      . 2 clouds of points : images did not match the code
        (negative coord impossible from rand())
      . First spiral: the image did not match with the example code:
        The code does not vary the size of dots.
      scatter3d(): last example:
       . p refered to nothing.
       . color() was called with RGB in [0,1] instead of in [0,255] => dark

  * UNIT TESTS: More than 50+50 tests added.

  * FEATURES ADDED:
      + colors identified with "#RRGGBB" or indices
      + options "smallOnTop" and "datatips"
        (documented only for scatter())

Change-Id: Id26797f8e713d7e3078031c8fc4d1db7c529606c