add caption tabindex and localized strings

bigbluebutton-client/locale/en_US/bbbResources.properties

bigbluebutton-client/resources/config.xml.template

bigbluebutton-client/resources/prod/layout.xml

...org/bigbluebutton/modules/caption/model/CaptionOptions.as

...rg/bigbluebutton/modules/caption/views/CaptionWindow.mxml

...c/org/bigbluebutton/modules/caption/views/OptionsTab.mxml

...nt/src/org/bigbluebutton/modules/caption/views/TextTab.as

...t/src/org/bigbluebutton/modules/chat/model/ChatOptions.as