Add trailing text to textlines, most useful for units.

common/lib/capa/capa/inputtypes.py

@@ -483,6 +483,7 @@ class TextLine(InputTypeBase):
             Attribute('dojs', None, render=False),
             Attribute('preprocessorClassName', None, render=False),
             Attribute('preprocessorSrc', None, render=False),
+            Attribute('trailing_text', ''),
         ]
 
     def setup(self):

common/lib/capa/capa/templates/textline.html

@@ -31,6 +31,9 @@
             style="display:none;"
         % endif
    />
+   % if trailing_text:
+   ${trailing_text}
+   % endif
 
       <p class="status">
         % if status == 'unsubmitted':