Use unconstrained quotes in reference manual

Prior to this commit, there were numerous places in the reference
manual, where we would see output similar to the following:

    BeanDefinition`s with the `ApplicationContext

This commit addresses this issue by using unconstrained quotes
(e.g., ++XYZ++s) instead of backticks (e.g., `XYZ`s) when the formatted
text is immediately followed by an "s".

This commit also corrects a few typos and corrects natural English
pluralization of Java code elements in the reference manual where
appropriate -- for example, "@Controllers" becomes "@Controller classes,
etc.

Issue: SPR-11650