Add error message to player-settings and weighted-settings pages if the call to /api/generate returns a non-2xx response code.

WebHostLib/templates/playerSettings.html

@@ -11,6 +11,7 @@
 {% block body %}
     {% include 'header/grassHeader.html' %}
     <div id="player-settings">
+        <div id="user-message"></div>
         <h1>Start Game</h1>
         <p>Choose the options you would like to play with! You may generate a single-player game from this page,
             or download a settings file you can use to participate in a MultiWorld. If you would like to make

WebHostLib/templates/weightedSettings.html

@@ -12,6 +12,7 @@
     {% include 'header/grassHeader.html' %}
     <div id="weighted-settings">
         <header id="user-warning"></header>
+        <div id="user-message"></div>
         <h1>Weighted Settings</h1>
         <div id="instructions">
             This page is used to configure your weighted settings. You have three presets you can control, which