Show an inspector with inputwidget when the user clicks a math
node. The data of the math equation is shown in the
edit box, it can re-render the math tag image when
the inspector is closed, and save the change when
saving the page.
TODO:
* Change the icon from link to math
* Translate title by translatewiki in i18n
* Other further UI improvements
Change-Id: I4d7533af25186cc39cc4bc6a4326d222ffd6db19
