New custom seekbar: more improvements

fix value txt being cutted when too long

allow to set a custom string to show instead of the
numeric value when value is defaultValue

res/values/cherish_attrs.xml

@@ -19,6 +19,7 @@
         <attr name="interval" format="integer" />
         <attr name="min" format="integer" />
         <attr name="units" format="string|reference" />
+        <attr name="defaultText" format="string|reference" />
     </declare-styleable>
 
     <!-- Value to pass to callback when restore button is pressed -->