Added the Plancake e-mail parser library to MediaWiki using Composer

The library was included earlier in BounceHandler/vendor/ but this seems to be the
right place to add the additional dependency. Made a specific snapshop of dev-master
branch to be cloned on composer run.
Pulled the plancake library directly from the Github Source

Bug: 72779
Change-Id: I5cc3d2eda7188628fd016950a16ffe63c2ae6f6f