Allow configuration of a default value for a label.

This change allows a project admin or owner to define a default value
(or score) for a label. The default value is set in the project configurations
file with a 'defaultValue' key.  The defaultValue must be within the range of
valid label values.  It is an optional label setting, if not defined the
defaultValue for the label will be 0.  When a defaultValue is defined, that
value will get set in the Reply dialog by default.  A defaultValue can be set
to a score that is outside of the permissible range for a user.  In that case
the score that will get set in the Reply box will be the next closes score
to the defaultValue.

feature: Issue 2041
Change-Id: I12dece29b043e09eaab62cdcf56146a1380041bc

Documentation/rest-api-changes.txt

diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 8f6b8a4..c172781 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -3093,6 +3093,8 @@
 |`value`       |optional|The voting value of the user who
 recommended/disliked this label on the change if it is not
 "`+1`"/"`-1`".
+|`default_value`|optional|The default voting value for the label.
+This value may be outside the range specified in permitted_labels.
 |===========================
 
 ==== Fields set by `DETAILED_LABELS`