add ubb__signin_margin

Author: partha-uber

core/src/main/res/values/dimens.xml

@@ -22,5 +22,6 @@
     <dimen name="ub__standard_padding">16dp</dimen>
     <dimen name="ub__small_padding">8dp</dimen>
 
+    <dimen name="ub__signin_margin">48dp</dimen>
     <dimen name="ub__progress_bar_height">32dp</dimen>
 </resources>