Add option to configure the file edit token timeout

[oanalavinia]

Right now, the token that authenticates the Collabora editing has a timeout of 1h. This value is not working for all use cases and most often can lead to major issues, see #37 for a detailed report.

I propose to have a configuration option in order to let administrators decide the token lifetime span.
Also, the best will be to increase the default to a higher value, since 1h is to short for the basic use of this app.

[oanalavinia]

I created a configuration option for token timeout, which will have a default value of 5 (hours)