Bugfix/documentation editor host undefined

[jykae]

Closes #1057

Proposed changes

• fix subscriptions for documentation editor
• show "Create documentation" section with link on API "Documentation" tab when Editor is enabled and host settings is set

[jykae]

For reviewer:
Documentation editor section would be available on "Documentation" tab of API in "Manage" modal when Editor settings are ok. For host try http://editor.apinf.io OR http://editor.swagger.io

[jykae]

Further notice:
I will put "Enabled" style the same way as it is with "Mail", so that these settings look consistent. Marking WIP..

[jykae]

@apinf/developers ready for review

[frenchbread]

Reviewing this PR.

@jykae While testing, I noticed that when incorrect url is provided the modal window instantly hides and the error text is not visible. Should we continue showing modal if there were a validation error?

[jykae]

@frenchbread Incorrect URL for editor in settings? I think it is admin responsibility to set up Apinf correctly. Or what incorrect URL you mean, something in modal?

[frenchbread]

Works good. Merging.

As discussed, potentially we can provide a select box with existing and know editors rather than making a user fill the url by himself. Also currently, any url, not related to editor can be stored.