Upgrade to asttokens 3.0, no longer need six (#498)

Also make assistant headers more obviously clickable

core/core_imports.txt

@@ -13,6 +13,5 @@ pyflakes
 pygments
 python_runner
 sentry_sdk
-six.py
 snoop
 stack_data

frontend/src/App.js

@@ -250,7 +250,7 @@ const Assistant = (assistant) => {
     <Collapsible classParentString="assistant-requirements card"
                  contentInnerClassName="assistant-content card-body"
                  trigger={<div className="card-header">
-                   <FontAwesomeIcon icon={faQuestionCircle}/> {terms.requirements}
+                   {terms.requirements}
                  </div>}
     >
       <p>
@@ -269,7 +269,7 @@ const Assistant = (assistant) => {
                  classParentString="assistant-assessment card"
                  contentInnerClassName="assistant-content card-body"
                  trigger={<div className="card-header">
-                   <FontAwesomeIcon icon={faListCheck}/> {terms.assessment} &nbsp;
+                   {terms.assessment} &nbsp;
                    {newMessages && <span className="badge badge-pill badge-danger">{terms.new}</span>}
                  </div>}
     >
@@ -278,7 +278,7 @@ const Assistant = (assistant) => {
     <Collapsible classParentString="assistant-hints card"
                  contentInnerClassName="assistant-content card-body"
                  trigger={<div className="card-header">
-                   <FontAwesomeIcon icon={faLightbulb}/> {terms.hints_and_solution}
+                   {terms.hints_and_solution}
                  </div>}
     >
       <HintsAssistant {...assistant}/>

frontend/src/css/main.scss

@@ -468,10 +468,22 @@
 .assistant {
   margin-top: 1em;
 
+  .card-header {
+    padding: .75rem 3.25rem;
+    background: rgba(0,0,0,0);
+  }
+
   .card__trigger {
     font-size: larger;
     position: relative;
 
+    cursor: pointer;
+    background: linear-gradient(rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.1));
+
+    :hover {
+      background: linear-gradient(rgba(0, 0, 0, 0.05), rgba(0, 0, 0, 0.15));
+    }
+
     // Font awesome icons
     svg {
       width: 2em;
@@ -482,8 +494,8 @@
       font-family: 'Tahoma', sans-serif;
       content: '^';
       position: absolute;
-      right: 20px;
-      top: 10px;
+      left: 20px;
+      top: 12px;
       display: block;
       transition: transform 300ms;
     }