Enabled restoring archived records

• Enabled restoring archived clients, invoice, quotes, payments and credits
• Added support for 10 new payment providers
• Enabled setting a fixed amount discount
• If invoice prefix is different than the quote prefix then the same number is used when cloning
• Recurring option is now hidden for existing invoices
• Invoices are now individualized for the selected contact
• Added support for negative line item amounts
• Created a setup page for self-hosters