Implement global regex/filter for validation of scoresheet and/or flight IDs

[prphntm63]

Submitted by Matt Herrold

• There is no validation on entry number format
• Should limit entry numbers to numeric only with a max length of 8 digits

Other thoughts:

• This should be configurable, as not all competitions may use a purely numeric entry number

[PH-Lazurous]

Want to keep this open, we need to add a scoresheet settings section in admin with this as one of the options.

[prphntm63]

I limited it to 6 alphanumieric chars for now in #70

[prphntm63]

But yes, let's leave it open and change AC to be "global app setting / regex to filter entry numbers"