Add uppy--hidden class

This commit removes .uppy-StatusBar.is-hidden and adds a common class .uppy--hidden

src/scss/_common.scss

@@ -18,6 +18,10 @@
   box-sizing: inherit;
 }
 
+.uppy--hidden {
+  display: none
+}
+
 // https://blog.prototypr.io/align-svg-icons-to-text-and-say-goodbye-to-font-icons-d44b3d7b26b4
 
 .UppyIcon {

src/scss/_statusbar.scss

@@ -16,10 +16,6 @@
   height: 0;
 }
 
-.uppy-StatusBar.is-hidden {
-  display: none;
-}
-
 .uppy-StatusBar.is-complete .uppy-StatusBar-progress {
   background-color: $color-green;
 }