fix(icon): Support non-qrc icons in a user location

Author: iBelieve

src/core/Icon.qml

@@ -63,10 +63,14 @@ Item {
             } else if (icon.source.indexOf('icon://') === 0) {
                 var name = icon.source.substring(7)
 
-                if (name)
-                    return "qrc:/icons/" + name + '.svg'
-                else
+                if (name) {
+                    if (Theme.iconsRoot.indexOf('qrc') != -1)
+                        return Theme.iconsRoot + '/' + name + '.svg'
+                    else
+                        return Theme.iconsRoot + '/' + name.replace('/', '_') + '.svg'
+                } else {
                     return ""
+                }
             } else {
                 return icon.source
             }

src/core/Theme.qml

@@ -79,6 +79,8 @@ Object {
         light: false
     }
 
+    property string iconsRoot: "qrc:/icons"
+
     /*!
        A utility method for changing the alpha on colors. Returns a new object, and does not modify
        the original color at all.