WebUI: Fix code indentation

Follow project coding style. Issue #2192.
WebUI: Fix increasing frequency of XHR requests

ajaxfn() is called every time the torrent list is filtered. This function
calls itself after a predefined amount of time by setting a timer. If
the function is called manually without destroying the timer, the
frequency of the XHR requests will increase.

Fix this by saving a reference to each timer that is created so that
they can be later destroyed.

Add also two helper functions to request updated data safely.
WebUI: Update title immediately when showing/hiding rates
WebUI: Keep current preference for the title style in a variable

Read persistent value only when required.
WebUI: Remove unused variable
WebUI: Use CSS to alternate row colors in transferlist

Keep the old code for IE < 9, the majority of the browsers
shouldn't need it.

Also, keep the CSS code in one place.