Support match, match aggregate, match group, and match group aggregate (#100)

## What is the goal of this PR?

We have updated protocol to support not only `match` queries, but also `match aggregate`, `match group`, and `match group aggregate`.

## What are the changes implemented in this PR?

- Extend the protocol by adding new message types: `Match.Aggregate`, `Match.Group`, and `Match.Group.Aggregate`
- Remove the ability to nest `AnswerGroup` which is no longer needed given the new answer structure.

Author: Ganeshwara Hananda

protobuf/answer.proto

@@ -24,25 +24,22 @@ import "protobuf/concept.proto";
 
 package grakn.protocol;
 
-message Answer {
-    oneof answer {
-        AnswerGroup answer_group = 1;
-        ConceptMap concept_map = 2;
-        Number number = 3;
-    }
-}
-
-message AnswerGroup {
-    Concept owner = 1;
-    repeated Answer answers = 2;
-}
-
 message ConceptMap {
     map<string, Concept> map = 1;
     string pattern = 2;
 }
 
+message ConceptMapGroup {
+    Concept owner = 1;
+    repeated ConceptMap concept_maps = 2;
+}
+
 message Number {
     string value = 1;
     // We use a string to contain the full representation of a number
 }
+
+message NumberGroup {
+    Concept owner = 1;
+    repeated Number numbers = 2;
+}

protobuf/query.proto

@@ -30,26 +30,29 @@ message Query {
     message Req {
         Options options = 1;
         oneof req {
-            Graql.Delete.Req delete_req = 100;
-            Graql.Define.Req define_req = 101;
-            Graql.Undefine.Req undefine_req = 102;
-            Graql.Match.Req match_req = 103;
-            Graql.Insert.Req insert_req = 104;
+            Delete.Req delete_req = 100;
+            Define.Req define_req = 101;
+            Undefine.Req undefine_req = 102;
+            Match.Req match_req = 103;
+            MatchAggregate.Req match_aggregate_req = 104;
+            MatchGroup.Req match_group_req = 105;
+            MatchGroupAggregate.Req match_group_aggregate_req = 106;
+            Insert.Req insert_req = 107;
         }
     }
 
     message Res {
         oneof res {
-            Graql.Delete.Res delete_res = 100;
-            Graql.Define.Res define_res = 101;
-            Graql.Undefine.Res undefine_res = 102;
-            Graql.Match.Res match_res = 103;
-            Graql.Insert.Res insert_res = 104;
+            Delete.Res delete_res = 100;
+            Define.Res define_res = 101;
+            Undefine.Res undefine_res = 102;
+            Match.Res match_res = 103;
+            MatchAggregate.Res match_aggregate_res = 104;
+            MatchGroup.Res match_group_res = 105;
+            MatchGroupAggregate.Res match_group_aggregate_res = 106;
+            Insert.Res insert_res = 107;
         }
     }
-}
-
-message Graql {
 
     message Match {
         message Req {
@@ -60,6 +63,36 @@ message Graql {
         }
     }
 
+    message MatchAggregate {
+        message Req {
+            string query = 1;
+        }
+
+        message Res {
+            Number answer = 1;
+        }
+    }
+
+    message MatchGroup {
+        message Req {
+            string query = 1;
+        }
+
+        message Res {
+            repeated ConceptMapGroup answers = 1;
+        }
+    }
+
+    message MatchGroupAggregate {
+        message Req {
+            string query = 1;
+        }
+
+        message Res {
+            repeated NumberGroup answers = 1;
+        }
+    }
+
     message Insert {
         message Req {
             string query = 1;