Reuse endpoint strings

[Citrullin]

Description

At the moment the endpoint strings are written multiple times. This can get reduced.
For example, in the generated code

const coap_resource_t _wot_coap_resources[] = {
   {"/led/rmtoggle", COAP_POST, wot_led_rmtoggle_handler, NULL},
   {"/led/status", COAP_GET | COAP_PUT, wot_led_status_handler, NULL},
   {"/led/toggle", COAP_POST, wot_led_toggle_handler, NULL}
};

wot_td_uri_t wot_td_config_init_action_affordance_1_int_affordance_form_0_href = {
   .value = "/led/rmtoggle",
};

wot_td_uri_t wot_td_config_init_action_affordance_0_int_affordance_form_0_href = {
   .value = "/led/toggle",
};

wot_td_uri_t wot_td_config_init_prop_affordance_0_int_affordance_form_0_href = {
   .value = "/led/status",
};