[!!!][+FEATURE] Extbase (Configuration): Made it possible to override controller...

[!!!][+FEATURE] Extbase (Configuration): Made it possible to override controller and action from FlexForm by defining a FlexForm field "switchableControllerActions" which is a semicolon-separated list of Controller->Action combinations. Also, all flexform values are merged on top of the framework configuration. This change is not backwards-compatible in case you used FlexForm settings. Before this change, a flexform setting "foo" has  been merged onto "settings.foo". Now, the flexform setting needs to be called "settings.foo" to be merged correctly into the settings (note the prefixing). This enables to override ALL TypoScript configuration from FlexForms, not just extension specific settings. Resolves #3348.