Move heatmap visualization to new script endpoint

[guerler]

Moves heatmap visualization to new script endpoint. Instead of having two separate heatmap variations (one with and one without clustering operation), the two have been combined into a single visualization. This PR also fixes several issues regarding zooming, job execution, and properly saving the visualization.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[itisAliRH]

Awesome, thanks @guerler!