Extend FROM EMAIL setting to components

The option to define a FROM email address should include the ability to have it be used for all component receipts (contribution/event/membership/pledge/case/etc.)

Currently, if a user registers someone for an event through the backend, the email receipt comes from the logged in user. Many organizations strongly prefer the email be sent from the main organizational address.

An option should be included in the FROM email setting to have it apply to all component mailings, in which case it overrides the user from email. If unset, the logged in user's address is used.