create namespace for plugins within Xinha namespace

[ray]

currently all plugins are simple functions, i.e. they are in the global (window) scope. This bad style as it requires deployers to take care not to have functions by the same name.

I propose creating a dedicated namespace Xinha.plugins. Plugins should then be written using this pattern

//wrap in a function that is executed immediately to encapsulate variables
(function(){
  Xinha.plugins.PluginName = PluginName; //connect to the plugins namespace
  function PluginName(editor)
  {
    //proceed normally
  }
})()

[ray]

rev [1079]