Improve mobile layout a bit (fixes #123)

frontend/src/pages/HomePage.module.less

@@ -1,9 +1,11 @@
+@import "styles.less";
+
 .welcomeMap {
   height: 60rem;
   max-height: 70vh;
   position: relative;
 
-  @media screen and (max-width: 767px) {
+  @media @mobile {
     margin: -35px -32px 0 -32px;
     max-height: 70vh;
   }

frontend/src/pages/SettingsPage.tsx

@@ -45,7 +45,7 @@ const SettingsPage = connect((state) => ({login: state.login}), {setLogin})(func
 
   return (
     <Page>
-      <Grid centered relaxed divided>
+      <Grid centered relaxed divided stackable>
         <Grid.Row>
           <Grid.Column width={8}>
             <Header as="h2">Your profile</Header>

frontend/src/pages/TrackEditor.tsx

@@ -95,7 +95,7 @@ const TrackEditor = connect((state) => ({login: state.login}))(function TrackEdi
 
   return (
     <Page>
-      <Grid centered relaxed divided>
+      <Grid centered relaxed divided stackable>
         <Grid.Row>
           <Grid.Column width={10}>
             <Header as="h2">Edit {track ? track.title || 'Unnamed track' : 'track'}</Header>

frontend/src/pages/TrackPage/TrackPage.module.less

@@ -1,13 +1,24 @@
+@import "styles.less";
+
 .stage {
   position: relative;
   margin-bottom: 32px;
 }
 
-.details.details {
-  position: absolute;
-  width: 320px;
-  top: 16px;
-  right: 16px;
-  max-height: calc(100% - 32px);
-  overflow: auto;
+@media @desktop {
+  .details.details {
+    position: absolute;
+    width: 320px;
+    top: 16px;
+    right: 16px;
+    max-height: calc(100% - 32px);
+    overflow: auto;
+  }
+}
+
+@media @mobile {
+  .details > :global(.ui.segment) {
+    box-shadow: none;
+    border: none;
+  }
 }

frontend/src/styles.less

@@ -9,3 +9,6 @@
 @secondaryColor: @obsColorG1;
 
 @menuHeight: 50px;
+
+@mobile: ~"screen and (max-width: 767px)";
+@desktop: ~"screen and (min-width: 768px)";