Dev guide: List the different OAuth applications created for CATcher

Let's briefly describe the different OAuth applications that we are using for development and actual usage (shown below)

We can also link to GitHub docs that explain the general process of creating an OAuth application.

Let's add this to the "Project management" section of the Dev guide.

Start in the Dev guide's "Project management" section and review the OAuth applications shown in the issue image. Add brief descriptions of the applications used for development and actual usage, plus a link to GitHub's OAuth application documentation. Done means the section clearly documents these applications and the creation process.

Written by the indexing model from the issue text.