Switch to hmm for Haxe dependency management

[jonasmalacofilho]

hmm can control the required versions of haxelibs and install/update all of them with a single command.

In this state, generator/hmm.json will already act as documentation on what libraries to install, and from where.

---

~to-do~ for another PR:

• [x] push suitable hmm.json
• [x] switch the server build to hmm
• ~document how to deal with the remaining manual dependencies (node, haxe, ???)~
• ~document how to prepare a build environment (hmm and npm)~
• ~document how/when to update a build environment (hmm and npm)~

~extras (maybe for #139 or a new PR): for another PR as well~

• ~document how to build manu~
• ~document how to run the unit tests~
• ~document how to package and install manu~

Documentation goals moved to #155 ...

[jonasmalacofilho]

~Missing documentation...~

Documentation goals moved to #155 ...