Tweak: improves the templates number/date functions

[alexmigf]

#659

This PR improves the templates display functions:

New functions:

$this->number( $document_type );
$this->date( $document_type );
$this->number_title();
$this->date_title();
$this->due_date_title();

Deprecated functions:
get_invoice_number
invoice_number
get_invoice_date
invoice_date

Changed functions:
get_number: now includes $formatted bool arg
get_date: now includes $formatted bool arg

[MohamadNateqi]

LGTM!

[MohamadNateqi]

@alexmigf Do you have any idea how the customer could raise this error? Since it seems they didn't have the Pro extension.

[alexmigf]

Not yet, it's still in discussion in the ticket.

[alexmigf]

@MohamadNateqi it seems that the issue was caused by another plugin that creates a receipt document for our plugin. Anyway, I think we should go forward with this improvements which simplifies the number and date document functions. What you think?

[MohamadNateqi]

I think we should go forward with this improvements which simplifies the number and date document functions. What you think?

Totally agree. It's a good improvement.