Add tool for refreshing tile cache

[Carifio24]

pywwt now has the ability to ask WWT to refresh the tile cache (which deletes all tiles that have been downloaded and cached). This isn't something that should be needed often, but in case some tile fails to load (e.g. due to a network issue), this allows refreshing the cache rather than being stuck with a low-res tile. This PR exposes this functionality as a tool for the WWT viewer.

The icon is something that I grabbed from the Noun Project. If someone else has another icon idea I'm open to suggestions!

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.32%. Comparing base (f6f0135) to head (d5de837).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
glue_wwt/viewer/jupyter_viewer.py	0.00%	1 Missing ⚠️
glue_wwt/viewer/tools.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
+ Coverage   71.21%   71.32%   +0.10%     
==========================================
  Files          18       18              
  Lines        1063     1074      +11     
==========================================
+ Hits          757      766       +9     
- Misses        306      308       +2     

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[astrofrog]

Looks nice!