Towards 6.0, the next steps

[fabpot]

Next steps:

• replace the Swiftmailer even dispatcher by the Symfony one.

[stof]

@fabpot would it be worth refactoring Swiftmailer to stop using a static service locator in a weird way (look at how arguments are passed to the parent constructor all the time for instance) ?

[fabpot]

@stof sure, but we need Pimple first and I will create a PR for that (not finished yet)

[xdecock]

Dropping Magic codes? ( automatic text / plain => mixed/alternative when adding a text/html part ) code there is probably a few other sections that might benefit from simplification / transparency and removal of dormant bugs / code messing up with datas.