[model/events.xsd] updated based on new findings

Did some thinking, and this is what I came up with:

- PlayerInvited should really be called "InvitationMade". In analogy
  with method calls, the events should refer to the thing where the state
  changes. An invitation is affected by this event; players aren't.

- We do need an InvitationAccepted event, despite what we previously
  thought. We need it because we need something to invalidate the
  invitation for further AcceptInvitation commands, and only an event
  will do that.

model/events.xsd

@@ -23,7 +23,7 @@
     </xs:complexType>
   </xs:element>
 
-  <xs:element name="PlayerInvitedEvent">
+  <xs:element name="InvitationMadeEvent">
     <xs:complexType>
       <xs:all>
         <xs:element name="InvitationID" type="xs:int" />
@@ -36,26 +36,34 @@
     </xs:complexType>
   </xs:element>
 
-  <xs:element name="GameStartedEvent">
+  <xs:element name="InvitationRejectedEvent">
     <xs:complexType>
       <xs:all>
-        <xs:element name="GameID" type="xs:int" />
-        <xs:element name="FirstPlayerHandle" type="xs:string" />
-        <xs:element name="SecondPlayerHandle" type="xs:string" />
-        <xs:element name="Size" type="xs:int" />
-        <xs:element name="PlayerTimeLimit" type="xs:duration" />
+        <xs:element name="InvitationID" type="xs:int" />
       </xs:all>
     </xs:complexType>
   </xs:element>
 
-  <xs:element name="InvitationRejectedEvent">
+  <xs:element name="InvitationAcceptedEvent">
     <xs:complexType>
       <xs:all>
         <xs:element name="InvitationID" type="xs:int" />
       </xs:all>
     </xs:complexType>
   </xs:element>
 
+  <xs:element name="GameStartedEvent">
+    <xs:complexType>
+      <xs:all>
+        <xs:element name="GameID" type="xs:int" />
+        <xs:element name="FirstPlayerHandle" type="xs:string" />
+        <xs:element name="SecondPlayerHandle" type="xs:string" />
+        <xs:element name="Size" type="xs:int" />
+        <xs:element name="PlayerTimeLimit" type="xs:duration" />
+      </xs:all>
+    </xs:complexType>
+  </xs:element>
+
   <xs:element name="StonePlacedEvent">
     <xs:complexType>
       <xs:all>