Allow adding/removing multiple headers in one method call

It would be nice to have convenience methods to add and remove multiple headers in [InternetHeaders](https://github.com/javaee/javamail/blob/master/mail/src/main/java/javax/mail/internet/InternetHeaders.java) and subsequently [MimeMessage](https://github.com/javaee/javamail/blob/master/mail/src/main/java/javax/mail/internet/MimeMessage.java) and [MimeBodyPart](https://github.com/javaee/javamail/blob/master/mail/src/main/java/javax/mail/internet/MimeBodyPart.java).

These could include:
```
addHeader(Header header)
addHeadersWithHeaderList(List headers)
addHeadersWithStringList(List headers)
setHeader(Header header)
removeHeader(Header header)
removeHeadersWithHeaderList(List headers)
removeHeadersWithStringList(List headers)
```

Start by reviewing the existing header methods in InternetHeaders.java, MimeMessage.java, and MimeBodyPart.java. Compare their current APIs and determine the intended multiple-header operations and signatures; done means the agreed convenience methods are consistently specified across the three classes.

Written by the indexing model from the issue text.