Add visibility toggle

Full Changelog: v2.0...v2.1

v2.0

• new gfx.uibrowser (replacement of Matlab's old plotbrowser)
• user-defined keyboard shortcuts
• add slow zoom
• support KeyRelease event
• shortcut for toggling grid
• many bugfixes

Full Changelog: v1.0...v2.0

First release for Matlab Fileexchange

v1.0

examples, comments