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/problem_content_1240.html

@@ -0,0 +1,22 @@
+<h3 class="hd hd-3 problem-header">Problem Header</h3>
+
+<div class='problem-progress'></div>
+
+<div class="problem">
+  <p>${_("Problem Content")}</p>
+
+  <div class="action">
+    <input type="hidden" name="problem_id" value="1">
+
+    <input type="text" name="input_example_1.Test" id="input_example_1.Test" value="" class="math" />
+    <span id="display_example_1"></span>
+    <span id="input_example_1_dynamath"></span>
+
+    <input class="check" type="button" value="Check">
+    <input class="reset" type="button" value="Reset">
+    <input class="save" type="button" value="Save">
+    <button class="show"><span class="show-label">Show Answer(s)</span> <span class="sr">(for question(s) above - adjacent to each field)</span></button>
+    <a href="/courseware/6.002_Spring_2012/${ explain }" class="new-page">Explanation</a>
+    <div class="submission_feedback"></div>
+  </div>
+</div>