Support pulling of several inbox folders

[0xShiroKuma]

In order to apply different processing, it would be useful to be able to pull several inbox folders from the same email address. And in the future support several folders from different email address.

[ninSmith]

I implemented this in the branch 27: https://github.com/TheHive-Project/Synapse/tree/feature/27

Can you try ?

For the conf, do comma separated without space:

folder_name:folder1,folder2,folder3