"Add to favorites" functionality

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After this the user will get notifications about the region.

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On app load get push token.

• If token is different from locally saved token, delete old token from each favorite area-channel and add new

On add/remove favorite

• Add/remove saved token to corresponding area-channel
• Add/remove area from locally saved favorites

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Use native storage: http://ionicframework.com/docs/v2/native/nativestorage/