- Declaring an endpoint's scopes in a `before` block has proved to be
  unreliable. For example, if we're accessing the `API::Users` endpoint - code
  in a `before` block in `API::API` wouldn't be able to see the scopes set in
  `API::Users` since the `API::API` `before` block runs first.

- This commit moves these declarations to the class level, since they don't need
  to change once set.

Extended ProjectFinder in order to handle the following options:
 - current_user - which user use
 - project_ids_relation: int[] - project ids to use
 - params:
   -  trending: boolean
   -  non_public: boolean
   -  starred: boolean
   -  sort: string
   -  visibility_level: int
   -  tags: string[]
   -  personal: boolean
   -  search: string
   -  non_archived: boolean

GroupProjectsFinder now inherits from ProjectsFinder.
Changed the code in order to use the new available options.