Regenerate icon and splash image assets

[pkalita-lbl]

In working on #238 I noticed that our existing icon assets didn't follow some best practices regarding asset sizing. This made the image look a little "soft" in certain scenarios. Specifically, @capacitor/assets recommends starting with 1024x1024 PNG files, whereas the images in our assets directory were 512x512.

These changes:

• Add an SVG file that contains layers for both the light and dark logo variations. It uses the full color logo for the light variation and the monochromatic white logo for the dark variation.
• Update the PNG files in the assets folder to be 1024x1024 (exported from the SVG file).
• Regenerate the native project icon and splash images from the 1024x1024 PNG files (via @capacitor/assets)
• Add a README file to the assets folder to describe the regeneration process.