(#2898) - small edits to the docs

Major changes:

* Safari 8 doesn't use IndexedDB; corrected that.
* Browser adapter plugins are no longer "experimental"; let's just be honest: they pass the tests, but they don't work in Browserify.
* Recommending some browser extensions to clear site data; I find it really useful during development and it occurred to me that developers might not know about them.
* Random formatting fixes
Not sure we should recommend this as it removes the user's data too:
- Clear the browser's history
- Clear the browser's cache
- Clear the browser's cookies
- Clear the browser's list of downloaded files
- Clear the browser's stored form data and passwords