[add #146] Add a share button in paper page

The share button opens a popup.
This popup contains the paper permission manager.
Merge pull request #152 from tdurieux/share_paper

[add #146] Add a share button in paper page
[fix #156] Fix regression in paper option

The fix is quite simple, the problem is real however. The role saving
function must be actually executed for the roles to be persisted into
the database.

This bug only impacts the paper options screen, contributors can still
be added or removed by using the new "Share" menu in the paper editor.
Merge pull request #158 from satabin/fix/156-cannot-add-contributors

[fix #156] Fix regression in paper option
Add changelog
[#161] Add report issue and clone link in the configuration

Add two new optional configurations:
 - blue.client.issues-url: link to report issues
 - blue.client.clone-url: where the code can be found.

The client side configuration manager has been improve.
All configurations stored in AppConfig is now automatically available in the constant
config.