Impossible to save the edited file after leaving the collabora editor open for a longer period of time

[lucaa]

How to reproduce:

• open the editor for a file
• make some changes, save them with the save button from the Collabora editor
• make some more changes
• leave the editor open in a tab for some time
  • apparently, according to the code, it shouldn't matter what happens in the editor during this time: additional changes can be made, or no action, or even additional saves could happen
• click the "save" button from the Collabora editor

Expected result:

• the file is saved with the latest changes

Actual result:

• an error is displayed about an invalid token and the file cannot be saved (example in french):
  
• if the "close" button is used at this point to close the editor, all changes are lost and there is no warning about closing with unsaved changes.

[lucaa]

See the workaround from #36 (comment) for not losing the work that was done on the file in the collabora editor.

[oanalavinia]

NOTE that this issue was updated to not specify for how long you need to leave the editor open before you hit the problem. This was needed since after implementing #40, the default timeout value was moved to 5 hours, instead of 1. This value can be modified by administration.

I am not sure if now this isn't actually the expected behavior, to have a timeout for how long you can have an editor open.
My proposal as solution is to still have the possibility to renew the current editing session without hitting refresh. Maybe add some sort of a renew token button in the UI, which will do this silently at the user request. (maybe check #36 (comment))