Allow to upload with imgur or to use the base64 method 

Hi,
I am the maintainer of the strut package for YunoHost.
I have a user who posted an issue about imgur dependence. I have made a quick modification to allow the use of base64 method with small image. Now the user can choose between the 2 methods.

If you are ok to merge it, it should be cool.

Thanks for your work on Strut.