This commit introduces a loading indicator for cases where `icon.source`
is set (a custom image/icon) to improve UX of the component.
It also falls back to a letter identicon in case loading the image source
wasn't successful.
Usage:
```
StatusIconTabButton {
icon.source: "SOME URL THAT CAN'T BE RESOLVED"
icon.color: "red" // in case fallback is used, icon.color will be gray by default
name: "Some channel" // used to generated letter identicon as fallback
}
```
Closes#37
9b99d8a957