To manage all the optional dependencies and related code, Simple Java Mail should be split up into modules

[bbottema]

Currently the single main project Simple Java Mail contains all the code and optional dependencies. To better manage the code and dependencies and more clearly communicate these options to our users, Simple Java Mail should be split up into modules.

This could also solve all the cyclic dependencies between the modules and the main project.

[bbottema]

Ugh, code coverage with Code Climate, Codacy or Coveralls seems impossible with GIT submodules. Now it seems I broke the Codacy project board as well :/

edit 02-02-2019: files a ticket with Codacy to have the boards fixen...