refactor: glimmer migration

[GreatWizard]

Refactor

Glimmer migration (#179)

• Use glimmer component for the feature-controls component
• Use anglebracket syntax in tests
• Refactors test in order to mock services more clearly
• Prevent _normalizeFlag function to be renamed/removed in features service by adding a fallback to camelize
• Rename service feature-control-storage into feature-controls-storage (typo)
• Split acceptance tests depending of the context (localstorage or not)

[MrChocolatine]

-- Friendly remark --

In general ...args should be preferred over ...arguments, even if by convention the latter is used in Ember.js.
Reminder: arguments is not a real Array, ...args is.