Change input format of map component

[anders-kiaer]

Currently the Python side of the map component requires the input as images. In order to reduce probable duplication of code in containers - the map component might want to handle numpy array input, and then internally convert to base64-image before giving it to the React component.

This will also facilitate that max and minvalue used in colormap does not need to be specified explicitly by the containers.

[anders-kiaer]

This would probably have to be implemented as a static Python class function which facilitates the conversion (in order to remain true to the prop-update-machinery of Dash).

[anders-kiaer]

Also it would be nice to design a React component API such that we don't need to transfer the whole data json package every time something is added/removed/updated in the LayeredMap.

[anders-kiaer]

Moved to #110 for better overview. Closing this.