Create UI for CSV team management (#22310)

Adds "Manage" sub-tab to course "Teams" tab
with UI for downloading and uploading team
membership CSVs. The upload and download function-
ality are currently not implemented.

The new tab only appears when the user is course staff
and the course has at least one instructor-managed
team-set, which is not the case for any existing
courses, so not current course staff will see this
change.

This ticket will be followed-up upon in MST-44 and
MST-49.

MST-41

lms/static/lms/js/spec/main.js

@@ -819,6 +819,7 @@
         'teams/js/spec/views/edit_team_members_spec.js',
         'teams/js/spec/views/edit_team_spec.js',
         'teams/js/spec/views/instructor_tools_spec.js',
+        'teams/js/spec/views/manage_spec.js',
         'teams/js/spec/views/my_teams_spec.js',
         'teams/js/spec/views/team_card_spec.js',
         'teams/js/spec/views/team_discussion_spec.js',

lms/static/sass/views/_teams.scss

@@ -353,7 +353,29 @@
     }
   }
 
-  .team-profile {
+  .team-management {
+    padding: 1%;
+
+    h3, p, .action, .team-management-section {
+        margin-bottom: 2%;
+    }
+
+    .input-overlay-hack {
+      position: absolute;
+      height: 100%;
+      width: 100%;
+      opacity: 0;
+      top: 0;
+      left: 0;
+      cursor: pointer;
+    }
+
+    .upload-team-csv {
+      position: relative;
+    }
+  }
+
+  .team-profile, .team-management {
     .page-content-main {
       display: inline-block;
       width: flex-grid(8, 12);