Add a custom default avatar to the sddm-breeze theme.

Summary:
With commit 945a95d908b4544f7c5dea6caacffdc0f44cffcb SDDM will now support a custom default avatar in the next release. [[ 945a95d908 | Forgot the link. ]]

Before the patch:
{F5741458}
After tha patch:
{F5741459}

Note that the above is not quite the same as the logout screen thingy. But I am not sure how to make it render the image in a way that it does not quite touch the edge of the border.
To illustrate what I mean:
{F5741460}
With the logout screen the user icon is not touching the circle border.

Test Plan: Works for me

Reviewers: #plasma, #vdg, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D11057

sddm-theme/faces/.face.icon

@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 22 22">
+  <defs id="defs3051">
+    <style type="text/css" id="current-color-scheme">
+      .ColorScheme-Text {
+        color:#f2f2f2;
+      }
+      </style>
+  </defs>
+ <path 
+     style="fill:currentColor;fill-opacity:1;stroke:none" 
+     d="M 11 3 A 3.9999902 4.0000296 0 0 0 7 7 A 3.9999902 4.0000296 0 0 0 11 11 A 3.9999902 4.0000296 0 0 0 15 7 A 3.9999902 4.0000296 0 0 0 11 3 z M 11 4 A 3 3.0000296 0 0 1 14 7 A 3 3.0000296 0 0 1 11 10 A 3 3.0000296 0 0 1 8 7 A 3 3.0000296 0 0 1 11 4 z M 11 12 A 7.9999504 8.0000296 0 0 0 3.0722656 19 L 4.0800781 19 A 6.9999604 7.0000296 0 0 1 11 13 A 6.9999604 7.0000296 0 0 1 17.921875 19 L 18.929688 19 A 7.9999504 8.0000296 0 0 0 11 12 z "
+     class="ColorScheme-Text"
+     />
+</svg>