Allow re-writing the subject line on Inbound Email activities when filing on case via the File on Case button.

Often subject lines on inbound emails are of the form "Re: one more tihng", or even blank. Filing on a case as is is not ideal. But in order to make the filing feature work without potential data loss with the current architecture, editing the email itself is disabled.

Suggest adding a text field to the popup when you select the target case that allows you to specify another subject.