add new feature - avatar group

[ikesela]

CSS example:
`.avatar-group .avatar {
position: relative;
z-index: 2;
border: 2px solid #fff; }
.avatar-group .avatar:hover {
z-index: 3; }

.avatar-group .avatar + .avatar {
margin-left: -1rem; }`

Code Example:

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[lubber-de]

🤫 This is in progress....Wait for 2.9.0 😉