remover deprecation warning

"Mocha deprecation warning: Change `require 'mocha'` to `require 'mocha/setup'`."
improve notification tests not to fail when other error notification is already present
ensure logging is loaded only once
disable logging test

not to broke logging setting for test environment
it also removes deprecation warnings
remove deprecation warning, pdf mime type is already defined

removes "warning: already initialized constant PDF"
improving documentation, reverting changes in commented out tests
Merge pull request #1929 from pitr-ch/quick-fix/remove-deprecation-warnings

remove some deprecation warnings