Issue #2389455 by hussainweb, AjitS, Mile23, subhojit777, tibbsa, Ayesh: Clean-up system module test members - ensure property definition and use of camelCase naming convention

Issue #2453059 by Wim Leers: Set default render cache contexts: 'theme' + 'languages:' . LanguageInterface::TYPE_INTERFACE

Issue #2432837 by Wim Leers, Fabianx: Make cache contexts hierarchical (e.g. 'user' is more specific than 'user.roles')

Issue #2445743 by dawehner, Wim Leers: Allow views base tables and entity types to define additional cache contexts

Revert "Issue #2445743 by dawehner, Wim Leers: Allow views base tables and entity types to define additional cache contexts"

This reverts commit a87aff86.

Issue #2445743 by dawehner, Wim Leers: Allow views base tables and entity types to define additional cache contexts