Rosetta theme: Use wp_enqueue_style() for RTL stylesheet

[ocean90]

There is currently no easy way to bump the version of the rtl.css. The patch uses wp_enqueue_style() if is_rtl() is true and removes the locale_stylesheet action from wp_head.

[nacin]

OK.

[samuelsidler]

In 994:

Rosetta theme: Use wp_enqueue_style() for RTL stylesheet. Fixes #739. props ocean90