Added tests for uploading files

TODO: When deleting is available, test deleting uploaded files`

cms/djangoapps/contentstore/features/upload.feature

+Feature: Upload Files
+    As a course author, I want to be able to upload files for my students
+
+    Scenario: Users can upload files
+        Given I have opened a new course in Studio
+        And I go to the files and uploads page
+        When I upload the file "upload.feature"
+        Then I see the file "upload.feature" was uploaded
+
+    Scenario: Users can update files
+        Given I have opened a new course in studio
+        And I go to the files and uploads page
+        When I upload the file "upload.feature"
+        And I upload the file "upload.feature"
+        Then I see only one "upload.feature"

cms/djangoapps/contentstore/features/upload.py

+#pylint: disable=C0111
+#pylint: disable=W0621
+
+from lettuce import world, step
+import os
+
+
+@step(u'I go to the files and uploads page')
+def go_to_uploads(step):
+    menu_css = 'li.nav-course-courseware'
+    uploads_css = '.nav-course-courseware-uploads'
+    world.css_find(menu_css).click()
+    world.css_find(uploads_css).click()
+
+
+@step(u'I upload the file "([^"]*)"$')
+def upload_file(step, file_name):
+    upload_css = '.upload-button'
+    world.css_find(upload_css).click()
+
+    file_css = '.file-input'
+    upload = world.css_find(file_css)
+    upload._element.send_keys(os.getcwd() + '/' + file_name)
+
+    close_css = '.close-button'
+    world.css_find(close_css).click()
+
+
+@step(u'I see the file "([^"]*)" was uploaded')
+def check_upload(step, file_name):
+    index = get_index(file_name)
+    assert index != -1
+
+
+@step(u'I see only one "([^"]*)"$')
+def no_duplicate(step, file_name):
+    names_css = '.name-col > a.filename'
+    all_names = world.css_find(names_css)
+    only_one = False
+    for i in range(len(all_names)):
+        if file_name == all_names[i].html:
+            only_one = not only_one
+    assert only_one
+
+
+@step(u'I PAUSE')
+def pause(step):
+    from pdb import set_trace; set_trace()
+
+
+def get_index(file_name):
+    names_css = '.name-col > a.filename'
+    all_names = world.css_find(names_css)
+    for i in range(len(all_names)):
+        if file_name == all_names[i].html:
+            return i
+    return -1