README.md: add todo items for invoices.
Invoices: added possibility to create an invoice not linked to punches, and added possibility to edit/view an invoice (but saving the edited invoice is not yet implemented).
CRM/Timetrack/Case/Page/CaseView.php: added link to generate ODT invoices, improved UI for timetrack actions.
Merge branch 'master' of github.com:mlutfy/ca.bidon.timetrack