deleteaccountdialog: disable delete button when it's clicked
This is so that the user cannot accidentally click Delete again and delete another account. Also, show a BusyIndicator spinning wheel when Delete is clicked, so as to give the user visual feedback that something is happening. Also, set the account Id, best name, and whether it's a SIP account from outside when opening the dialog, so that they don't automatically change when the next account is selected if the user confirms the deletion of the current account. GitLab: #711 Change-Id: I4e93deb4f74257387884edc62d76a5b3cb58d845