改进评级用户level

1. Add jquery.js and word_operation.js to the static folder.

2. Changed the return type of the familiar, unfamiliar and deleteword methods of user_service.py.
    ```
    original: return redirect(url_for('userpage', username=username))
    now: return "success"
    ```
3. In order to get elements in JS to make ajax requests we add ids in userpage_get.html for familiar, unfamiliar, delete buttons and so on.

4. When the user's word book was retrieved, the list returned was already sorted in descending order of frequency, so redundant code was removed in userpage_get.html.

Co-authored-by: PeterQiu <www.1392993990@qq.com>
Co-authored-by: Lan Hui <1348141770@qq.com>
Reviewed-on: http://121.4.94.30:3000/mrlan/EnglishPal/pulls/30
Co-authored-by: 邱忠辉 <1392993990@qq.com>
Co-committed-by: 邱忠辉 <1392993990@qq.com>

@@ -81,3 +103,4 @@
     geometric = 1
     for date in sorted(d_user2.keys(), reverse=True): # most recently added words are more important while determining user's level
         lst = d_user2[date] # a list of words
+        #print(lst)

@@ -78,0 +87,4 @@
+            change_word=word[:-1]
+        elif word.endswith('ed'):
+            change_word=word[:-2]
+        elif word.endswith('en'):

@@ -78,0 +95,4 @@
+            if change_word==word2:
+                lst1[index]=change_word
+                break
+    return lst1   

@@ -78,0 +79,4 @@
+def stem_words(list_of_words):  # It reduces words to the root word (eg. ate, eaten -> eat; leaves, leaf -> leaf)
+    wnl = WordNetLemmatizer()
+    lst1 = [wnl.lemmatize(w) for w in list_of_words]
+    return [wnl.lemmatize(w, pos='v') for w in lst1]  # stem by verb: 'v' represents verb