Migrate Project structure to use gradle

[cedricziel]

The project depends on the toolbox and the annotation plugin, so this
will only ever build if they update first.

[cedricziel]

@Haehnchen There's many tests that are supposed to not run when PHPSTORM_ENV is set. How should we handle these? Am I right those are sketched and not ready yet? If yes, how should we handle them? By now, they break the build and they will surely annoy future contributors.

[cedricziel]

Two test classes were not found by the ant script glob. I renamed them in 68b83a5 to get into a state where we have been before and the build should become stable again for the 2017.3 line.

[Haehnchen]

@cedricziel tests about PHPSTORM_ENV can be disabled. simply they are not working without a full project right now.

[cedricziel]

@Haehnchen Alright, the PRs are all ready to be merged.

We should start with Haehnchen/idea-php-toolbox#79 and tag it with 0.4.7 or something else i can then adjust in the other PRs to.

Then Haehnchen/idea-php-annotation-plugin#110 needs another run on travis, but i expect it to be green as well.

After that, the main plugin (this PR) is next. The laravel plugin one is green as well.

Thx in advance!

[cedricziel]

@Haehnchen Upgraded to stable 2018.1 platform requirements, fixed 2 OpenAPI issues and it's green now.