Emit finished signal from AC derived classes

To avoid Agent destruction-in-use move emit finished from
setFinished to Agent methods. For other ACs emit from
aboutToFinish().

assignment-client/src/Agent.cpp

@@ -335,6 +335,7 @@ void Agent::scriptRequestFinished() {
         }
 
         setFinished(true);
+        emit finished();
     }
 
     request->deleteLater();
@@ -839,6 +840,7 @@ void Agent::aboutToFinish() {
 
     // destroy all other created dependencies
     DependencyManager::destroy<ScriptCache>();
+    DependencyManager::destroy<ScriptEngines>();
 
     DependencyManager::destroy<ResourceCacheSharedItems>();
     DependencyManager::destroy<SoundCache>();

assignment-client/src/assets/AssetServer.cpp

@@ -342,6 +342,7 @@ void AssetServer::aboutToFinish() {
     while (_pendingBakes.size() > 0) {
         QCoreApplication::processEvents();
     }
+    emit finished();
 }
 
 void AssetServer::run() {

assignment-client/src/entities/EntityServer.cpp

@@ -72,6 +72,8 @@ void EntityServer::aboutToFinish() {
     DependencyManager::get<ResourceManager>()->cleanup();
 
     OctreeServer::aboutToFinish();
+
+    emit finished();
 }
 
 void EntityServer::handleEntityPacket(QSharedPointer<ReceivedMessage> message, SharedNodePointer senderNode) {

assignment-client/src/scripts/EntityScriptServer.cpp

@@ -582,4 +582,6 @@ void EntityScriptServer::aboutToFinish() {
         _codec->releaseEncoder(_encoder);
         _encoder = nullptr;
     }
+
+    emit finished();
 }

libraries/networking/src/ThreadedAssignment.cpp

@@ -66,8 +66,6 @@ void ThreadedAssignment::setFinished(bool isFinished) {
 
             // call our virtual aboutToFinish method - this gives the ThreadedAssignment subclass a chance to cleanup
             aboutToFinish();
-
-            //emit finished();
         }
     }
 }

libraries/networking/src/ThreadedAssignment.h

@@ -25,7 +25,7 @@ public:
     ~ThreadedAssignment() { stop(); }
 
     void setFinished(bool isFinished);
-    virtual void aboutToFinish() { };
+    virtual void aboutToFinish() { emit finished(); };
     void addPacketStatsAndSendStatsPacket(QJsonObject statsObject);
 
 public slots: