Change NHS Number to IHI

[PhilBarrett]

We need to change the NHS number to the IHI number at the UI,middleware and backend. from 10 digits to 18 digits

[PhilBarrett]

Currently it can only cater for up to 16 digits

"The problem is that somewhere along the line the number is being treated as an integer - and the largest integer you can handle in JavaScript is 9007199254740991"

Workaround is to stick with max of 16 digits for demo purposes and not to go above number 9007199254740991 for the accounts

[kuvakina]

@PhilBarrett now we can create 18 digits for IHI#