Preview icon backport

[max-carroll]

Description

This is a backport of a PR already implemented implemented, but here's the description of that PR

I have created a new prop getPreviewIcon which allows you to pass your own function which determines which Preview Icon should be displayed for selected file.

I also added an example in the markdown as this was useful for testing, and thought it would also be useful so that people can see how to use the prop and a possible use case for it

• Fixes The preview Icon could be specific to the type of file (at the moment its just a paperclip) #149

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested

• Test A - Checked preview icons worked as before with Images and Non Images
• Test B - Checked bespoke functions work and correctly display a new icon as in the new example for PDFs, Audio etc...

Test Configuration:

• Browser:

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[panz3r]

LGTM 👍