[API] Completely dropped all scope-specific stuff.

 * There is no need for attribute scope entity. Previously it was needed for determining which type of attributes should be printed using variadic placeholder in string formatter (too many "special cases", right?). Now there are internal and external attribute scopes, which is handled automatically. Variadic placeholder prints only external attributes.
[Code Clean] Drop unnecessary function.
[Documentation] Style.
[Documentation] More verbose.
[Documentation] Style.
[Tasks] One task less.
[Unit Testing] Repository registration process has been tested.

 * One task less.
[Aux] More forward declarations.
[Feature] Added and tested logger concept.