[WIP] Feature/api v3 base

https://www.openproject.org/work_packages/8769
Try making the dependencies available to both Bundler groups, e.g.

```ruby
group :development, :test do
  gem 'pry-rails'
  gem 'pry-stack_explorer'
  gem 'pry-rescue'
  gem 'pry-byebug', :platforms => [:mri_20,:mri_21]
  gem 'pry-doc'
end
```