Make Global Property parsed and cached (not fetching and parsing every time)

TODO: this (GP_ENCOUNTER_TYPE_TO_VISIT_TYPE_MAPPING) Global Property should be parsed and cached (as a map) instead of fetching it and parsing it every time. (And we should have a global property change listener to recalculate it when that Global Property is changed.)
File: /api/src/main/java/org/openmrs/api/handler/ExistingOrNewVisitAssignmentHandler.java
Line: 80

You can look at: org.openmrs.api.GlobalPropertyListener and org.openmrs.api.impl.GlobalLocaleList