web: Make viewing the in-page documentation optional

After talking with @GirlBossRush, I realized that my architecture would be simplified by separating
the style controller from the renderer.  Lit uses Controllers just for that purpose, so:

1. A renderer that either puts down the button or puts down the documentation

2. A controller that monitors the button for its state and, when that state changes, updates the
   host's CSS to fit within the page correctly when the button is rotated.

3. Some helper styles the container needs to help the button display correctly.

Run the thing and click on the button.

This changes the look and feel of the application to a small degree. Screenshots may need to be
updated.

None.

\# What

\# Why

\# How

\# Designs

\# Test Steps

\# Other Notes

web/src/elements/SidebarHelp/SidebarHelp.css

@@ -0,0 +1,14 @@
+ak-sidebar-help-toggle {
+    display: none;
+}
+
+@media screen and (min-width: 768px) {
+    ak-sidebar-help-toggle {
+        display: block;
+    }
+}
+
+ak-sidebar-help-toggle.pf-m-width-default {
+    background-color: inherit;
+    max-width: 3rem;
+}