make download function work with non-US-ASCII characters

[lopatoid]

Fixed #441 . After this fix, you'll be able to use "download" function of Remi to download files with non-ASCII characters in the filename.

[dddomodossola]

Hello @lopatoid thank you very much. Can you please make it compatible with python2 ? I know that the world should switch to python3, but there are still lot of devices compatible only with python2 and remi aims to work everywhere.

[lopatoid]

I can, but the latest git version of Remi doesn't work with python2

python2 examples/widgets_overview_app.py
........
remi.server.ws   INFO     connection established: ('127.0.0.1', 41096)
remi.server.ws   DEBUG    handle
remi.server.ws   DEBUG    handshake
remi.server.ws   INFO     handshake complete
remi.server.ws   DEBUG    send_message: 0140142837... -> ('127.0.0.1', 41096)
remi.server.ws   ERROR    Error managing incoming websocket message
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/remi-2022.7.27-py2.7.egg/remi/server.py", line 175, in read_next_message
    opcode = head[0] & 0b1111
TypeError: unsupported operand type(s) for &: 'str' and 'int'
remi.server.ws   DEBUG    ws ending websocket service

[dddomodossola]

Hello @lopatoid thank you. Now I am abroad, I will review your changes when back to home on 4 March.