Bump to JavaMail 1.6 and get rid of outdated JARs in lib/

[cbarcenas]

Might as well bump the pom.xml to JavaMail 1.6.x.

Also, seem to be even older versions of JavaMail creeping around the lib/ directory. Are these used anywhere?

[bbottema]

Haha, no. They are for convenience only (many years ago it was a little difficult to find the right version). I think it can be removed now...

[bbottema]

Released as 5.0.0.rc1-SNAPSHOT. Add OSS' snapshots repo to find it in Maven.