BUG: Set the summary fields of UserDefinedForm_EmailRecipient dynamically via config system

You can't dynamically expose statics; that's a no-op in 3.1
Merge pull request #112 from oddnoc/fix-summary-fields

BUG: Set the summary fields of UserDefinedForm_EmailRecipient
Don't clear statics as public for 3.1 compatibility
BUG Fixed incorrect static member declaration
- Changed configurable static variables to private as per recent API updates to 3.1
- Use of statics as configurable variables replaced with config api usage
Merge branch '3.1-config-compatibility-fixes' of git://github.com/tractorcow/silverstripe-userforms into tractorcow-3.1-config-compatibility-fixes
Updating composer.json to require 3.1
MINOR: Update SS version
Merge pull request #115 from ARNHOE/patch-4

MINOR: Update SS version
FIX: validate required fields even with rules. (Fixes #116)
Remove test for old submissions tab