[invoice-improvements] Improve invoice page, so they can be duplicated and sent easily (Privátny)

We want to easily duplicate and send invoices. Michal currently must copy previous invoice, create a new invoice and paste information there. Then he send invoice over an email.

Go to /invoices/detail/1826, it can look like this: https://drive.google.com/…XExghxz/view?…

Create two new buttons next to "Download PDF" (see screenshot):

• duplicate - duplicates this invoice. It will redirect to invoices/create and pre-fill all fields and checkboxes, except dates (Issue date, Taxable supply date, Due date).
• send by e-mail - it will redirect us to a page with a form. The form has field e-mail and a button to send this PDF by e-mail. (sending PDF through email is in the system already).

Send by email features:

• create a new DB table, like invoice_email, where will be cols invoice_id, sent (datetime, when an email was sent), email (address)
• print information sent and email to detail of an invoice (see screenshot). Print only the last record, not all of them.

Email Subject:

Splátka rekvalifikačního kurzu

Email Message:

Dobrý den,
v příloze mailu Vám dle splátkového kalendáře zasíláme fakturu za rekvalifikační kurz Programátor www aplikací. Mockrát díky za úhradu a přeji pěkný den

+ fancy podpis