add regex url check before joining channel

stylesheets/_session.scss

@@ -503,7 +503,7 @@ label {
 .message-selection-overlay {
   display: none;
   position: absolute;
-  right: 15px;
+  right: 10px;
   left: 15px;
 
   .close-button {

ts/components/session/LeftPaneChannelSection.tsx

@@ -302,6 +302,8 @@ export class LeftPaneChannelSection extends React.Component<Props, State> {
       return false;
     }
 
+    const regexURL = /(http:\/\/www\.|https:\/\/www\.|http:\/\/|https:\/\/)?[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(:[0-9]{1,5})?(\/.*)?/;
+
     if (channelUrlPasted.length <= 0) {
       window.pushToast({
         title: window.i18n('noServerURL'),
@@ -312,6 +314,16 @@ export class LeftPaneChannelSection extends React.Component<Props, State> {
       return false;
     }
 
+    if (!regexURL.test(channelUrlPasted)) {
+      window.pushToast({
+        title: window.i18n('noServerURL'),
+        type: 'error',
+        id: 'connectToServerFail',
+      });
+
+      return false;
+    }
+
     // TODO: Make this not hard coded
     const channelId = 1;
     this.setState({ loading: true });