Better support for Google Colab

[CuloArdido]

When installing pywb in Google Colab following this procedure¹ and after starting the server², the pages I try to access within a collection appear blank because the scripts and CSS links point by default to http://colab.research.google.com/ instead of where they should be³.

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1. Before installing pywb you should run this command to avoid a dependency conflict:

   !pip uninstall flask nbconvert -y
   

   Then the procedure is the same as in the documentation but prepending a ! before each command.

2. To start the server, the following must be executed:

   from google.colab.output import eval_js
   # Show the link through which the user can access to the server
   print(eval_js("google.colab.kernel.proxyPort(8080)"))
   !wayback -p 8080

   The -p parameter would normally not be needed unless the user wants to use a port other than 8080.

3. This is usually something like https://someid-port-colab.googleusercontent.com