Add some feedback when performing some actions (#552)

* Add a way to display flash messages

* Make the flash messages look nice

* Add actual feedback messages

* cargo fmt

* Move flash messages to PlumeRocket

And add trait to convert PlumeRocket to BaseContext

* Remove useless lifetime

static/css/_header.scss

@@ -76,15 +76,28 @@ header {
 
 .messages {
   & > * {
-      padding: 1em 20%;
+    padding: 1em 20%;
+    margin: 0;
+    max-width: initial;
+    font-weight: bold;
   }
 
   p.error {
-    color: $red;
+    color: darken($red, 20%);
     background: lighten($red, 40%);
     margin: 0;
     max-width: initial;
   }
+
+  p.warning {
+    color: darken($yellow, 20%);
+    background: lighten($yellow, 40%);
+  }
+
+  p.success {
+    color: darken($green, 20%);
+    background: lighten($green, 40%);
+  }
 }
 
 // Only enable label animations on normal screens

static/css/_variables.scss

@@ -8,6 +8,8 @@ $white: #F4F4F4;
 $purple: #7765E3;
 $lightpurple: #c2bbee;
 $red: #E92F2F;
+$yellow: #ffe347;
+$green: #23f0c7;
 
 // Fonts