Add sharing links for the posts

[mountainbug95]

Fixes #198

[regisphilibert]

Thanks for thinking about a config but two things:

1. We need a "disable" sharing config, as I believe by default, user will want those on and we can't expect them to turn on the setting on each post.
2. I don't think the user will want to limit the number of share services added to their post, for many: the more the better. But if we decide to allow this it should be on the project level. I don't see any reason why user would want Facebook on one post and not the other.

@budparr for 2. do you think we should allow user to disable a given share service? I don't but I might be missing some use cases.

[budparr]

I agree. I don't think that fine-tuned disabling is necessary

[regisphilibert]

@mountainbug95 Thanks a lot for this! After discussion could you though:

1. remove the "per post" config and replace it by a disable_share set to false on one example post.
2. Rework your code for this param test and add all 3 service no matter what.

🙏