Tidying CHEBGUI.

* Use just one string for the 'Ultraspherical' button, so that
  we don't get weird results when resizing font.

* Moving some initialization steps into the @chebguiController
  class. Makes code easier to maintain via version control.

* Getting rid of a redundant 'envelope' button from the .fig file
  that we were not using anymore.
Merge branch 'development' of ssh://github.com/chebfun/chebfun into fix-chebgui-initFields
Merge pull request #905 from chebfun/fix-chebgui-initFields

Some CHEBGUI tidying.