Eliminate all uses of raster graphics in the UI

[wetneb]

This issue is here to keep track of all the raster images that we include as part of OpenRefine's UI.
We would like to migrate them to SVGs instead, for better scalability and flexibility of styling (for instance to implement a dark mode).

As we work on migrating away from those raster images, we would like to preserve (or improve) the consistency of the visual style of OpenRefine, but we don't expect pixel-perfect replacements at all.
Any help to replace those PNG files would be most welcome, even without making the associated code changes: feel free to just upload the proposed SVG replacements as a comment on this issue and someone else can take care of integrating them in the code base.

Note: in the graphics folder we have some PSD files which you could also work from (they are likely in higher resolution)

This is the current list of PNGs:

• main/webapp/modules/core/images/close.png
• main/webapp/modules/core/images/slider-handle.png
• main/webapp/modules/core/images/menu-dropdown.png
• main/webapp/modules/core/images/scatterplot-icons.png
• main/webapp/modules/core/images/leftpanel-showhide.png
• main/webapp/modules/core/images/minimize-map.png
• main/webapp/modules/core/images/star-flag-map.png
• main/webapp/modules/core/images/right-arrow.png
• main/webapp/modules/core/images/menu-opener.png
• main/webapp/modules/core/images/close-map.png
• main/webapp/modules/core/images/down-arrow.png
• main/webapp/modules/core/images/favicon.png
• main/webapp/modules/core/images/facet-resize-handle.png
• main/webapp/modules/core/images/logo-gem-126.png - Use SVG logo and icons instead of png #6316
• main/webapp/modules/core/images/checks-map.png
• main/webapp/modules/core/images/star.png
• main/webapp/modules/core/images/logo-openrefine-550.png - Use SVG logo and icons instead of png #6316
• extensions/database/module/images/more-option-horiz-16.png
• extensions/database/module/images/more_option-vert-16.png
• extensions/gdata/src/com/google/refine/extension/gdata/logo-openrefine-550.png - Use SVG logo and icons instead of png #6316
• extensions/wikibase/module/images/Critical.png -> to be vectorized by Closes #5702, wikibase old looking UI on warnings. #6535
• extensions/wikibase/module/images/Information.png -> to be vectorized by Closes #5702, wikibase old looking UI on warnings. #6535
• extensions/wikibase/module/images/close-map.png
• extensions/wikibase/module/images/Warning.png -> to be deleted by Closes #5702, wikibase old looking UI on warnings. #6535
• extensions/wikibase/module/images/Wikibase_logo.png
• extensions/wikibase/module/images/wikidata.png
• extensions/wikibase/module/images/Important.png -> to be vectorized by Closes #5702, wikibase old looking UI on warnings. #6535
• graphics/dmg_background/dmg_background.png -> can be deleted
• graphics/row-groups.png -> can be deleted

And GIFs:

• main/webapp/modules/core/images/large-spinner.gif - see Swap gif loading spinners to CSS based ones #5902
• main/webapp/modules/core/images/small-spinner.gif - see Swap gif loading spinners to CSS based ones #5902

Pinging @cooperzoe, since this work is relevant to the production of vector icons for the operations, some of which will be based on existing icons taken from the UI (which therefore need vectorizing in the process).