combine all 1.x doc sets into a single dropdown option

First comment:

• [ ] call out 1.5 beta on the 1.4 whats new page.
• [ ] copy release notes from previous versions on the 1.4 release notes page.
• [ ] add contextual info to new feature pages to explain when a particular feature was introduced.
• [ ] add dropdown for SG config docs (#782).
• [ ] ask web team to hide 1.1.1, 1.2 and 1.3 from dropdown.
• [ ] rename 1.4 dropdown value to 1.x
• [x] combine swagger versions on a single page

see other comments: https://github.com/couchbaselabs/couchbase-mobile-portal/issues/804