feat(loading): add loading indicator component and styles

this is the initial commit - still needs work

references #5426

ionic/components/loading/test/basic/styles.css

@@ -0,0 +1,56 @@
+.custom-spinner-container {
+  position: relative;
+  display: inline-block;
+  box-sizing: border-box;
+}
+
+.custom-spinner-box {
+  position: relative;
+  box-sizing: border-box;
+  border: 4px solid #000;
+  width: 60px;
+  height: 60px;
+  animation: spin 3s infinite linear;
+}
+
+.custom-spinner-box:before {
+  content: '';
+  position: absolute;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%);
+  box-sizing: border-box;
+  border: 4px solid #000;
+  width: 40px;
+  height: 40px;
+  animation: pulse 1.5s infinite ease;
+}
+
+.wp .custom-spinner-box,
+.wp .custom-spinner-box:before {
+  border-color: #fff;
+}
+
+@-webkit-keyframes pulse {
+  50% {
+    border-width: 20px;
+  }
+}
+@keyframes pulse {
+  50% {
+    border-width: 20px;
+  }
+}
+
+@-webkit-keyframes spin {
+  100% {
+    -webkit-transform: rotate(360deg);
+            transform: rotate(360deg);
+  }
+}
+@keyframes spin {
+  100% {
+    -webkit-transform: rotate(360deg);
+            transform: rotate(360deg);
+  }
+}