add test of current issue start and due date datepicker (#14024)
replace non ASCII literal to hexadecimal at ApplicationHelperTest
include Redmine::I18n in ApplicationHelperTest
backout r11875 ApplicationHelperTest change
Include Redmine::I18n in helpers tests.
Code cleanup.
Merged r11850 from trunk (#14051).
Merged r11851 from trunk (#14023).
Merged r11843 from trunk (#13910).