Updated the code and made some improvements to the feedback writer helper.

The first commit of this branch adds some changes that have been introduced in SVN, all the subsequent commits introduce the following changes:
* The 'Send more requests' link now works as expected
* The freezing feedback button no longer freezes
* When no feedback text is present a proper error is displayed
* The thank you message is more easily distinguishable
* The the outgoing email no longer uses HTML entities in the title
* The newly added requests are shown below without a page reload
* The feedback error is displayed only once, replacing the old if necessary
* The feedback helper is closed properly if the post is published
* Sequential feedback requesting replaces placeholders properly 
* The WH_VERSION constant is used properly
* Creating the anonymous link updates the feedback table
* The counter image is included with a defined constant rather than hardcoded
* The visual styles are improved to use the WP styles and colors
* The plugin code brought up to the WP coding style (indentation and class names)
* The RTL styles are updated
* The jQuery objects for element queries that always return the same set are now cached
* The feedback experience on handheld devices is overhauled