Add Links to Hosted Docs about how to obtain OAuth Credentials

[KurtStam]

This is a...

[*] Feature request
[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Documentation issue or request

The problem

When starting to use Twitter or Salesforce the enduser needs to provide OAuth credentials. We should add a link (with configurable base path) to the specific doc page on how to obtain these credentials.

So for instance for Twitter the source doc is:
https://github.com/syndesisio/syndesis/blob/master/doc/shared/register_with_twitter.adoc

On Fuse we should link to:
https://access.redhat.com/documentation/en-us/red_hat_fuse/7.0/html/integrating_applications_with_ignite/connecting-to-applications#connecting-to-twitter

and on Syndesis to
https://syndesis.io/documentation/en-us/red_hat_fuse/7.0/html/integrating_applications_with_ignite/connecting-to-applications#connecting-to-twitter

And I guess we have maybe parameterize the version in the path too.

In addition this requires use to render the ascii doc and push them to the syndesis.io repo.

[KurtStam]

Is related to syndesisio/syndesis.io#86

[stale]

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