Use i18n_string() directly instead of webform_tt()

I'm thinking of submitting a patch for webform to update webform_tt() for the i18n_string API update from last spring (http://drupal.org/node/1534468).

I think this should module should just use i18n_string() directly since it's declared as a dependency. Using i18n_string() directly instead of the webform_tt() wrapper would allow this module to pass options to i18n_string() when necessary, as shown in http://drupalcode.org/project/webform_localization.git/commit/0f142fc.

I'd be happy to roll a patch.

Related issues:
#1796748: Translation of markup component: HTML is parsed an printend out
#1781266: Unnecessary check_plain() for radio labels and select options via i18n_string()