New functions ‘Back’ and ‘Next’ extension

[codinachssm]

New functions ‘Back’ and ‘Next’ in reference to the extent that the user sees on the map.
It is very useful in SITMUN2 to go back to what the user was viewing and to be able to redo forward.

[fjlopez]

Marta, use the template for new features:

**Is your feature request related to a problem? Please describe.**
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**Describe the solution you'd like**
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**Describe alternatives you've considered**
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**Additional context**
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[codinachssm]

Is your feature request related to a problem? Please describe.
There is no problem, is a new functionality.

Describe the solution you'd like
In SITMUN2 we have the ‘Previous Extension’ (zoom and extension) and ‘Next Extension’ (zoom and extension) buttons that allow the user to go to the previous zooms performed and also to the subsequent zooms (viewing scales through which the user has passed).
It is like navigating pages forwards and backwards in a web browser, but in this case it is the zoom of the map that changes (backwards and forwards).

Describe alternatives you've considered
We would like a similar funcionality in SITMUN3.

Additional context
In SITMUN2:
Previous zoom:

Next zoom: