refactor(core): BaseCatcher added

Env-agnostic logic from Catcher in @hawk.so/javascript moved in new abstract BaseCatcher so general logic (breadcrumbs management, user management, context management, message pre-processing and sending, and other utilities) may be reused in other platform-specific implementations.

Browser-specific logic (UI-framework integrations, window event listeners, ConsoleCatcher) remain in original Catcher in @hawk.so/javascript.

Author: Reversean