invoice 6.x-1.1

* Improved user experience, the form is no longer submitted the enter key is pressed. So an invoice item can be added whith the tab and enter key.
* Fixed regression bug: Set template on the invoice creation form is broken
* Updated translation files
* Fixed issue #719586: place dompdf in libraries folder
* Fixed issue #342664: Scripting error, can't add invoice items (Added support for clean urls off)
* Refactored invoice.js
* Cancel button when editing invoice item
* Confirm message when clicking on a delete icon
* After adding an invoice item move the cursor back to the invoice item description field
* Removed unused/old menu items in invoice_menu()
* Fully implemented permission "administer own invoices"
* Fixed issue #784530: Change of the owner of an invoice do not to change the owner of the invoice items
* Fixed issue #917230: Uninstall does not remove persistent variables
* Fixed issue #604198: PDF invoice name is not formatted
* Fixed issue #671658: Requires PHP5 - but not stated as requirement
* An invoice doesn't have revisions, so the revision information fieldset must be hidden.
* Fixed issue #671664: Uninstall does not work
* Fixed bug: Invoice prefix is based on the current time, this must be the invoice creation time.
* Fixed bug: Weight column was shows up after an invoice item when editing an invoice. This is not fully implemented yet and must not appear in the way it does now.