refactor: move xmodule folder to root

- Moving xmodule folder to root as we're dissolving sub-projects of common folder in edx-platform
    - More info: https://openedx.atlassian.net/browse/BOM-2579
- -e common/lib/xmodule has been removed from the requirements as xmodule has itself become the part of edx-platform and not being installed through requirements
- The test files common/lib/xmodule/test_files/ have been removed as they are not being used anymore

xmodule/js/fixtures/codeinput_problem.html

@@ -0,0 +1,21 @@
+<div id="textbox_101" class="capa_inputtype textbox cminput">
+  <label class="problem-group-label" for="cm-textarea-101">question label here</label>
+  <textarea rows="40" cols="80" name="input_101"
+            aria-label="python editor"
+            aria-describedby="answer_101"
+            id="input_101"
+            tabindex="0"
+            data-mode="python"
+            data-tabsize="4"
+            data-linenums="true"
+  >write some awesome code</textarea>
+  <span class="cm-editor-exit-message capa-message" id="cm-editor-exit-message-101">
+    Press ESC then TAB or click outside of the code editor to exit
+  </span>
+
+  <div class="grader-status" tabindex="-1">
+      <span id="status_101" class="correct" aria-describedby="input_101">
+          <span class="status sr">correct</span>
+      </span>
+  </div>
+</div>