Label for colour bar

[numeredev]

DESCRIPTION

What does your feature request improve on? Please describe.
Many times, the information encoded in the colour bar is not the same as the z value of the shown data. Therefore it is important to label the colour bar directly.

Describe the solution you'd like
Add an option clabel=LABEL for labeling the colourbar.

Additional context
Add any other context or screenshots about the feature request here.

(Do not write below this line)

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DEVS' SECTION

ANALYSIS

(Describe, what's the issue and which changes have to be made)

IMPLEMENTATION STEPS

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• Implement the necessary changes in a new branch created here on GitHub
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DOCUMENTATION STEPS

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• Update the changes log
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PULL REQUEST

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