Update english.php

Added "Submit" text to language file for buttons.
Update contact.tpl

Changed button from "Continue" to "Submit"
Update contact.php

Changed submit button language call.
Update return_form.tpl

Changed return form button from "Continue" to "Submit"
Update return.php

Changed language call for return form submission button from "Continue" to "Submit"
Added Custom Heading Title in Welcome module and rename module
code optimization
Merge pull request #1693 from stan-bg/patch-15

code optimization
Merge branch 'master' of git@github.com:opencart/opencart.git
Merge pull request #1694 from steven-wm/master

Fixes a typo on the product return page.
Merge branch 'master' of git@github.com:opencart/opencart.git
Added missing required class on address form.
more api work done
Merge branch 'master' of https://github.com/opencart/opencart
Fixed return history comments not being added.

Added prevent default action for FF browsers.
Merge branch 'master' of git@github.com:opencart/opencart.git
Fixed filter form validation message display. Verified white space cannot be used.
Merge branch 'master' of git@github.com:opencart/opencart.git
Fixed sort order on category list
Changed the links in the currency dropdown to use the <button> tag