Test error response for invalid children
Validate WP children

Originially, this method was defined in a WP patch in OpenProject Backlogs.
Move WP move test to spec and update its specification

With the additional validation of a WP's children, a move of a WP to another
project is only valid if cross project relations are allowed. The old test
didn't consider that setting and just assumed that a WP move is valid across
project borders in any case (even if cross project relations are forbidden).
Adapt cukes to child WP validation
Merge pull request #2315 from opf/fix/17318_error_message_on_invalid_parent

17318 error message on invalid parent
Refactor version property tests
Test that version value is empty if version is not set
Detect empty version id correctly
Merge pull request #2317 from opf/fix/17665_unassigned_version_has_no_empty_value

17665 Unassigned version has no empty value
Re-generate Coderay syntax highlighting styles

Coderay 1.0+ now uses more descriptive class names.
We use the default (alpha) styles:

`coderay stylesheet > app/assets/stylesheets/coderay.css`

Hotfix # 17114

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Test that non-existing WP status returns only one validation error
Check if status exists before validating the transition
Merge pull request #2321 from opf/hotfix/17114-syntax-highlighting-missing-styles
Merge branch 'release/4.0' into dev
Merge pull request #2322 from opf/fix/17441_fix_status_validation_messages

17441 Fix status validation messages
add users editable support