Add sqlalchemy into pip

[baonq-me]

This error happen on Ubuntu 16.04

$ sage web_server.py -p 80

Building Maxima command completion list (this takes
a few seconds only the first time you do it).
To force rebuild later, delete /home/sage/.sage//maxima_commandlist_cache.sobj.
AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz
Done!

Building R command completion list (this takes
a few seconds only the first time you do it).
To force rebuild later, delete /home/sage/.sage//r_commandlist.sobj.
Traceback (most recent call last):
  File "web_server.py", line 153, in <module>
    app = SageCellServer(args.baseurl, args.dir)
  File "web_server.py", line 82, in __init__
    db = __import__('db_' + config.get('db'))
  File "/home/sage/sagecell/db_sqlalchemy.py", line 9, in <module>
    from sqlalchemy import create_engine, Column, Integer, String, DateTime
ImportError: No module named sqlalchemy

[novoselt]

I am a bit puzzled why this is not in the build instructions and it seems that it has never been there...

Thanks a lot for trying to follow the instructions and submitting a fix!