Switch migration icon to svg (#15954)

Followup on https://github.com/go-gitea/gitea/pull/15952, use SVG for migration icon.

<img width="541" alt="Screen Shot 2021-05-23 at 00 26 12" src="https://user-images.githubusercontent.com/115237/119242417-c1a37600-bb5d-11eb-9f97-a80aa89741ee.png">
<img width="540" alt="Screen Shot 2021-05-23 at 00 25 39" src="https://user-images.githubusercontent.com/115237/119242419-c2d4a300-bb5d-11eb-9792-1e6e4092c9f9.png">

web_src/less/_base.less

@@ -1041,7 +1041,7 @@ a.ui.card:hover,
 
   .migrate {
     color: var(--color-text-light-2) !important;
-    opacity: .5;
+
     a {
       color: var(--color-text-light) !important;
 
@@ -1770,6 +1770,10 @@ a.ui.basic.label:hover {
   }
 }
 
+.migrate .svg.gitea-git {
+  color: #f05133; /* from https://upload.wikimedia.org/wikipedia/commons/e/e0/Git-logo.svg */
+}
+
 .ui.popup {
   background-color: var(--color-body);
   color: var(--color-secondary-dark-6);

web_src/svg/gitea-git.svg

@@ -1 +1 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 48 48" width="64px" height="64px"><path fill="#F4511E" d="M42.2,22.1L25.9,5.8C25.4,5.3,24.7,5,24,5c0,0,0,0,0,0c-0.7,0-1.4,0.3-1.9,0.8l-3.5,3.5l4.1,4.1c0.4-0.2,0.8-0.3,1.3-0.3c1.7,0,3,1.3,3,3c0,0.5-0.1,0.9-0.3,1.3l4,4c0.4-0.2,0.8-0.3,1.3-0.3c1.7,0,3,1.3,3,3s-1.3,3-3,3c-1.7,0-3-1.3-3-3c0-0.5,0.1-0.9,0.3-1.3l-4-4c-0.1,0-0.2,0.1-0.3,0.1v10.4c1.2,0.4,2,1.5,2,2.8c0,1.7-1.3,3-3,3s-3-1.3-3-3c0-1.3,0.8-2.4,2-2.8V18.8c-1.2-0.4-2-1.5-2-2.8c0-0.5,0.1-0.9,0.3-1.3l-4.1-4.1L5.8,22.1C5.3,22.6,5,23.3,5,24c0,0.7,0.3,1.4,0.8,1.9l16.3,16.3c0,0,0,0,0,0c0.5,0.5,1.2,0.8,1.9,0.8s1.4-0.3,1.9-0.8l16.3-16.3c0.5-0.5,0.8-1.2,0.8-1.9C43,23.3,42.7,22.6,42.2,22.1z"/></svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 48 48" width="64px" height="64px"><path d="M42.2,22.1L25.9,5.8C25.4,5.3,24.7,5,24,5c0,0,0,0,0,0c-0.7,0-1.4,0.3-1.9,0.8l-3.5,3.5l4.1,4.1c0.4-0.2,0.8-0.3,1.3-0.3c1.7,0,3,1.3,3,3c0,0.5-0.1,0.9-0.3,1.3l4,4c0.4-0.2,0.8-0.3,1.3-0.3c1.7,0,3,1.3,3,3s-1.3,3-3,3c-1.7,0-3-1.3-3-3c0-0.5,0.1-0.9,0.3-1.3l-4-4c-0.1,0-0.2,0.1-0.3,0.1v10.4c1.2,0.4,2,1.5,2,2.8c0,1.7-1.3,3-3,3s-3-1.3-3-3c0-1.3,0.8-2.4,2-2.8V18.8c-1.2-0.4-2-1.5-2-2.8c0-0.5,0.1-0.9,0.3-1.3l-4.1-4.1L5.8,22.1C5.3,22.6,5,23.3,5,24c0,0.7,0.3,1.4,0.8,1.9l16.3,16.3c0,0,0,0,0,0c0.5,0.5,1.2,0.8,1.9,0.8s1.4-0.3,1.9-0.8l16.3-16.3c0.5-0.5,0.8-1.2,0.8-1.9C43,23.3,42.7,22.6,42.2,22.1z"/></svg>