Added icons and modified manifest.json

[madhav6ram]

Fixes #125 Added icons into assets and updated manifest.json

Describe your changes in detail Added the icons of 16, 48px and updated 128px icon to make it more clear by cropping the text. Everything is placed in the images sub directory of /assets. The manifest.json file is updated to match the source of the new icons.

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.

SWOC Participation

• Name: Madhav Ram
• Discord Username: Madhav#7781
• [x] I have included the issue number in my PR