BUG Fixing plural_name messing up singular words ending in "e" (#3251)

This would ideally be fixed with the ability to use an external library
like gettext, but that's an API change. This for now fixes the issue
where a singular like "Page" returns "Pags" for the plural name.
Update 5-dataobject-relationship-management.md

Fixed two small mistakes:

"select one the the mentors" -> "select one of the mentors"
WYSIWIG -> WYSIWYG
Merge pull request #3485 from dpenas/patch-1

Update 5-dataobject-relationship-management.md
Fixes a bug that ignored any overridden path for assets/error-404.html etc
Merge pull request #3489 from markguinn/patch-error-path

Fixes a bug that ignored any overridden path for assets/error-404.html (etc)
Update searchcontext.md with &hellip; showing ???
Merge pull request #3492 from nhorstmeier/patch-2

Update searchcontext.md &hellip; showing ???
MINOR: Fixed copyright year
Merge pull request #3402 from halkyon/plural_fix

BUG Fixing plural_name messing up singular words ending in "e" (#3251)
Fix for Versioned->allVersions to work with new ORM
Restructured Imagick to contain an instance of Imagick, rather than extending it.
Fail gracefully when trying to start a new Imagick object. This is more consistent with GDBackend.

Fixes #3441
FIX: only react to left-clicks on GridField.
Refactored CSV export functionality to sit in it's own class.

Relates to #2802 #2431#3408
type hint boolean instead of bool
PHPDoc and instantiation updates
Merge branch 'fixes/versioned-join' into 3.1-jtch