Improve headings/decriptions on Identities page

[runboxdave]

https://runbox.com/app/account/identities

Change heading "Aliases" to "Identities for Aliases" (preferred) or "Alias Identities".

Remove the text under "Aliases" and replace it with the following.

"Aliases are extra email addresses that deliver to your account, just as your main username/email address does. Below are identities you can use if you want to send messages from your aliases. These identities can be customised by adding a different From Name, Signature or Reply-to address. You can also change the Runbox domain an alias uses. You can't delete these identities as they are tied to your aliases but you can manage your aliases by going to Alias Administration."

Under Other Identities replace text with.

"Other Identities can be used when you want to send from addresses that are not part of your Runbox account. Adding this kind of address (e.g. a work email address) will require verification via email that you have access to that account. You can also use Other Identities if you need additional identities for you Runbox email addresses."