Icons specifications

# Icons specification for Asset Registry
### Format
- .png

### Size
- 537x537 pixels

### Transparency and colors
- Make sure the logos within the icon are not transparent, otherwise they'll change color based on the various apps background colors
- Make sure the borders are visible and result in the intended visual effect, irrespectively of the background color of the apps where the icon will be displayed (i.e. no molding in the background)

### Padding
- no padding on the longest edge,
- icons should only have some padding on their shorter edge to have them fit within the 537x537 square. Inspect the two examples below with some graphic tool suite
L-BTC has some padding to the left and right, because height>width
USDt ha some padding above and below because width>height