Implemented some enhancement request and fixed some bugs

Fixed #2 : Variables are not recognized when inside a rule token
Fixed #15 : Rule: rete attributes are lost when a new ontology is created
Fixed #14 : ReteNetwork: Format rules must not be added to Rete network
Fixed #16 : DefConcept: Variables are not recognized when they are keyword arguments
Fixed #4 : Comparison are not correctly set when comparison property is a concept
Fixed #14 : Parser: merge FunctionParser.NamesNode and ExpressionParser.NamesNode
Fixed #18 : Parser: Add SourceCodeNode test to UnrecognizedNodeParser
Fixed #20 : At startup Number concept is saved in db a numerous number of time
Fixed #21 : CacheManager: I can remove all elements from a ListIfNeededCache and fill it again
Fixed #22 : CacheManager: I can remove all elements from a SetCache and fill it again
Fixed #23 : HistoryManager: history() no longer works
Fixed #24 : HistoryManager: history() no longer works after creating an exec rule
Fixed #25 : SheerkaMemory: Use MemoryObject instead of sheerka.local
Fixed #26 : Debugger: add the list all available services..
Fixed #27 : CONCEPTS_GRAMMARS_ENTRY does not seems to be in use any more
Fixed #28 : Give order to services

src/cache/ListIfNeededCache.py

@@ -15,7 +15,7 @@ class ListIfNeededCache(BaseCache):
             if isinstance(self._cache[key], list):
                 self._cache[key].append(value)
             else:
-                self._cache[key] = [self._cache[key], value]
+                self._cache[key] = value if self._cache[key] is Removed else [self._cache[key], value]
         else:
             self._sync(key)
 
@@ -28,7 +28,7 @@ class ListIfNeededCache(BaseCache):
                 if isinstance(self._cache[key], list):
                     self._cache[key].append(value)
                 else:
-                    self._cache[key] = [self._cache[key], value]
+                    self._cache[key] = value if self._cache[key] is Removed else [self._cache[key], value]
             else:
                 self._cache[key] = value
         self._add_to_add(key)

src/cache/SetCache.py

@@ -19,9 +19,12 @@ class SetCache(BaseCache):
 
     def _put(self, key, value, alt_sdp):
         if key in self._cache:
-            if value in self._cache[key]:
+            if self._cache[key] is Removed:
+                self._cache[key] = {value}
+            elif value in self._cache[key]:
                 return False
-            self._cache[key].add(value)
+            else:
+                self._cache[key].add(value)
         else:
             self._sync(key)
 
@@ -31,7 +34,10 @@ class SetCache(BaseCache):
                     self._cache[key] = sheerka_deepcopy(previous)
 
             if key in self._cache:
-                self._cache[key].add(value)
+                if self._cache[key] == Removed:
+                    self._cache[key] = {value}
+                else:
+                    self._cache[key].add(value)
             else:
                 self._cache[key] = {value}