Various bugs in the new Rights Management UI

While checking the new RMUI, I found and fixed several bugs/improvements, like:

• Changing the checkbox state should be done when receiving a confirmation message from the server, not when sending the request
• Clicking twice on a checkbox should not send two requests (twice while the checkbox is in the same state, not twice for changing the state two times)
• Events that don't change the filters shouldn't trigger a refresh (like pressing shift when the username filter has focus)
• Computing the displayed range from the scroll position was incorrect
• When updating the scrollbar dimensions, also update the scrollbar position
• Added lots of jsdoc, comments and todos
• Replaced the triplicated UI code (from adminglobalrights, adminspacerights and editrights) with only one rightsUI.vm template
• Don't send back and forth the list of displayed right levels, but use a local javascript variable
• Replace many areas of 7-fold duplicated code (once for each right) with foreach-es
• Replace particular right listing with one variable listing the displayed rights
• Made the Ajax table a bit more generic (XWiki-independent)
• Various javascript coding techniques improvements
• Fixed existing rights detection when more than one object for that person/group exists (use right lists updated for each object, instead of returning the string found in the last matching object), and only return true for deny when both allow and deny rules exist for the same right
• Fixed out-of-order response bugs (XWIKI-1849 and XWIKI-1843)
• When changing a right, also invalidate the fetch cache