Add a possibility to define high priority bundle

[estambakio-sc]

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ExtProjectId	JCCMMN-01
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It is needed to add a possibility to define a high priority bundle, which has higher priority than messages retrieved using register method.

The goal is to be able to give I18nManager a bundle of messages from a remote source of truth. If the requested key is present in this outer bundle, it is used instead of inner bundles. If not - I18nManager performs its own regular logic.

Details of implementations:

• add a function property to I18nManager constructor. This function takes locale and returns a bundle of messages for this locale (of type object)

• in getMessage method check for this function and if it exists then try to get the message using this function. If the message is not defined afterward, proceed with regular logic inside I18nManager.