'validate=required' doesn't work for number fields

[snemarch]

When adding a new row, validate=required fails for number field. Blank fields get the value '0'.

Demo here.

[kerro]

If a field number isn't filled, the field value is set to 0 and passes the validation

return parseInt(this.insertControl.val() || 0, 10) in jsgrid.field.number.js

[tabalinas]

I propose to consider this as a by design. The reason is that number field is defaulted to 0. Thus I don't see any feasible fix w/o a breaking change. So if you want to validate number field, you need to use another validator min.
Of course, it should be specified in docs.

[tabalinas]

Reopen the issue. If that one #125 will be fixed, we can fix this issue also.