fix: Reduce number of thumbnails created for admin, avoid admin thumbnails for svg files

[fsbraun]

Description

Over the years, several thumbnail file sizes for the filer admin have accumulated:

• 16x16, 32x32, 64x64
• 40x40/80x80 (current table listing)
• 75x75 for detail views
• 160x160 (current icon listing)
• 180x180 formerly used in the admin widget

This PR reduces the thumbnail sizes to two

• FILER_TABLE_ICON_SIZE = 40 for table listings plus twice the value for detail views
• FILER_THUMBNAIL_ICON_SIZE = 120 for the thumbnail view

No thumbnails are generated for SVG files shown in the admin.

This PR fixes #1489 and reduces the amount of storage used up for thumbnails used by the filer admin interface.

Currently, the icon sizes are also hard-coded into the css. The next step will be to make them html attributes and have dynamic css that adjusts to the attributes.

Related resources

• Uploading bigger SVG files blocks the UI #1489
• #...

Checklist

• I have opened this pull request against master
• I have added or modified the tests when changing logic
• I have followed the conventional commits guidelines to add meaningful information into the changelog
• I have read the contribution guidelines and I have joined #workgroup-pr-review on
  Slack to find a “pr review buddy” who is going to review my pull request.

[vinitkumar]

Just one minor feedback. Otherwise, this looks excellent. Great work as always @fsbraun :)