Refactor lookup providers

- Create lookup strategy object to handle several provider
- New root ID server provider
- Refactor code into appropriate classes

src/main/groovy/io/kamax/mxisd/lookup/PriorityLookupStrategy.groovy

@@ -0,0 +1,38 @@
+package io.kamax.mxisd.lookup
+
+import io.kamax.mxisd.api.ThreePidType
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.stereotype.Component
+
+@Component
+class PriorityLookupStrategy implements LookupStrategy {
+
+    @Autowired
+    private List<ThreePidProvider> providers
+
+    @Override
+    Optional<?> find(ThreePidType type, String threePid) {
+        if (ThreePidType.email != type) {
+            throw new IllegalArgumentException("${type} is currently not supported")
+        }
+
+        providers.sort(new Comparator<ThreePidProvider>() {
+
+            @Override
+            int compare(ThreePidProvider o1, ThreePidProvider o2) {
+                return Integer.compare(o2.getPriority(), o1.getPriority())
+            }
+
+        })
+
+        for (ThreePidProvider provider : providers) {
+            Optional<?> lookupDataOpt = provider.find(type, threePid)
+            if (lookupDataOpt.isPresent()) {
+                return lookupDataOpt
+            }
+        }
+
+        return Optional.empty()
+    }
+
+}