Add submit button component and style it.

frontend/src/app/components/submit-button/submit-button.component.scss

@@ -0,0 +1,43 @@
+button {
+    padding: .8em 1.2em;
+    border-radius: 10em;
+    border: none;
+    background-color: #3f51b5;
+    color: white;
+    transition: background-color .2s ease-in-out;
+    position: relative;
+
+    &:hover {
+        background-color: #5b6ed8;
+        cursor: pointer;
+    }
+
+    &.secondary {
+        color: #3f51b5;
+        background-color: white;
+
+        &:hover {
+            background-color: #f2f4ff;
+            cursor: pointer;
+        }
+    }
+
+    &:disabled {
+        background-color: #6d7ac5;
+        cursor: not-allowed;
+    }
+
+    mat-spinner {
+        position: absolute;
+        top: calc(50% - 12px);
+        left: calc(50% - 12px);
+    }
+}
+
+:host ::ng-deep .spinner circle {
+    stroke: white;
+}
+
+:host ::ng-deep .spinner.secondary circle {
+    stroke: #3f51b5;
+}