Chore:: Plugin tmpl override path corrected

Removed payplans constant and assumption. New assumption is any plugin
tmpl can be overrided by adding a folder plg_type_name to
template/template-name/html

Refer : #31
Chore:: Remove PAYPLANS Constants and J1.5 support

Refer #31 (reverted from commit f1194caf45417b25cd5e0dd9152d9b2197d33d6f)