Add inputmode="verbatim" to the textarea

This is to prepare for the upcoming implementation in IE10 and Blink (see https://code.google.com/p/chromium/issues/detail?id=244688), as well as the current implementation in Mozilla (which uses x-inputmode).

See also https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/KjKEZ5Ga3k8