Added jQuery Migrate to fix WYMeditor on higher versions of jQuery

This pull request addresses issue #365.

Because the `jQuery.browser` feature of jQuery has been deprecated and removed from jQuery starting in version 1.9.1, WYMeditor completely breaks and fails almost all of its tests on these higher versions of jQuery. By adding jQuery Migrate, `jQuery.browser` and other deprecated and removed features are restored to those higher versions of jQuery, allowing WYMeditor to run successfully with those versions.

From my testing with jQuery Migrate, WYMeditor now passes all of its tests in Chrome 27 and all but one test (that was failing with or without jQuery Migrate) in Firefox 21 using any version of jQuery from 1.5.0 to 1.9.1. Before, WYMeditor was failing almost all tests in both browsers using version 1.9.1 and failing a plethora of tests in Chrome 27 using version 1.8.3, so the addition of jQuery Migrate fixed the problem. It should be noted, however, that both browsers were still failing 12 or 13 tests using any version of jQuery higher than 1.9.1.

I also updated the docs and README with documentation on how to include jQuery Migrate in the page integration of WYMeditor.