various fixes for the metrics screen

add the missing 'usage' key and value in i18n files
rename wrong overriding threadDump assignation in angularJS scope
use right key in thread dump view for 'runnable' (from 'waiting')
change translate method to prevent bug in IE11 (see http://stackoverflow.com/questions/20647572/angularjs-v1-2-5-script-error-with-textarea-and-placeholder-attribute-using-ie11#answer-23574588)