Add placeholder icons & logos

[frenck]

Proposed change

This PR adds in the placeholder icons & logos. These will be used when a logo or icon for an integration is missing (and no fallback is available).

Type of change

• Add a new logo or icon for a new integration
• Add a missing icon or logo for an existing integration
• Replace an exiting icon or logo with a higher quality version
• Removing an icon or logo

Additional information

• This PR fixes or closes issue: fixes #
• Link to code base pull request:
• Link to documentation pull request:
• Link to integration documentation on our website:

Checklist

• The added/replaced image(s) are PNG
• The added/replaced image(s) are in the rRGB color space
• Icon image size is 256x256px (icon.png)
• hDPI icon image size is 512x512px for (icon@2x.png)
• Logo image size has min 128px, but max 256px, on the shortest side (logo.png)
• hDPI logo image size has min 256px, but max 512px, on the shortest side (logo@2x.png)

[github-actions]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 33.9%, saving 18.15 KB

Filename	Before	After	Improvement
src/_placeholder/icon.png	8.75 KB	5.35 KB	-38.8%
src/_placeholder/icon@2x.png	15.25 KB	10.37 KB	-32.0%
src/_placeholder/logo.png	9.26 KB	5.79 KB	-37.5%
src/_placeholder/logo@2x.png	20.30 KB	13.89 KB	-31.6%