Disable "lost password" feature, breaks on "php -S"

PHP's built-in webserver doesn't reliably expose SCRIPT_NAME,
see https://github.com/silverstripe/silverstripe-framework/issues/2580.
This breaks URL routing on /Security/passwordsent/admin%40test.com
GridField 'Add existing' action styling improvements
Email fluent API regression (fixes #2581)
Merge pull request #2582 from kinglozzer/2567-add-existing-gridfield-styling

GridField 'Add existing' action styling improvements (fixes #2567)
Merge pull request #2557 from camspiers/template-parser-configurable

Feature to allow changing the SSTemplateParser used in SSViewer
Merge pull request #2520 from wilr/destructivestyles

Style destructive actions destructively
MINOR typo where display_errors wasn't checked properly
Merge pull request #2584 from ss23/patch-3

MINOR typo where display_errors wasn't checked properly
FIX: Move stage choosing into a pre-request filter.

This ensures that the correct stage is selected, even if the request
does not come through the model as controller system. This fixes an
issue where custom controllers would always be on the "Stage" stage.
FIX: Move stage choosing into a pre-request filter.

This ensures that the correct stage is selected, even if the request
does not come through the model as controller system. This fixes an
issue where custom controllers would always be on the "Stage" stage.
Merge pull request #2585 from ss23/3.1-staging-fix

FIX: Move stage choosing into a pre-request filter.
Merge pull request #2586 from ss23/3.0-staging-fix

FIX: Move stage choosing into a pre-request filter.
MINOR typo where display_errors wasn't checked properly
Adjust UploadField edit form size

Thanks @kinglozzer for getting this started.
Fixes https://github.com/silverstripe/silverstripe-cms/issues/878
Replaces https://github.com/silverstripe/silverstripe-framework/pull/2221
Removed deprecated log/email logic from Debug (fixes #2573)

Was deprecated in 2009 with a682ab9c0e211167984b76790fb1458aae7ead7c,
and removed in 2012 with 9eca2d676f9278ba528cb2ea6be4151703ed8fc2
Merge pull request #2575 from dhensby/patch-2

FIX #2496 `ConfirmedPasswordField` mismatch passwords saved
Merge pull request #2526 from clyonsEIS/3.1

Add backwards compatibility for has_extension
Merge pull request #2537 from wilr/membervalidator

FIX: Use Injector API for managing Member_Validator instance.
Merge pull request #2395 from ARNHOE/patch-1

i18n documentation - added note for caching in multi language modules
FIX: Allow TreeDropdownField to open upwards (fixes #2188)