add pveIntegerField and use it

add pveIntegerField and use it

this adds a subclass of Ext.form.field.Number with the settings for
Integers (allowDecimals: false and allowExponential: false and default
step size 1)

and use it where we only accept integers

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>