Add missing files

Temporary and Reference variable have a specific classes for the SSA slithIR version

slither/slithir/variables/reference_ssa.py

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+'''
+    This class is used for the SSA version of slithIR
+    It is similar to the non-SSA version of slithIR
+    as the ReferenceVariable are in SSA form in both version
+'''
+from .reference import ReferenceVariable
+from .variable import SlithIRVariable
+
+class ReferenceVariableSSA(ReferenceVariable):
+
+    def __init__(self, reference):
+        super(ReferenceVariableSSA, self).__init__(reference.node, reference.index)
+
+        self._non_ssa_version = reference
+
+    @property
+    def non_ssa_version(self):
+        return self._non_ssa_version

slither/slithir/variables/temporary_ssa.py

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+'''
+    This class is used for the SSA version of slithIR
+    It is similar to the non-SSA version of slithIR
+    as the TemporaryVariable are in SSA form in both version
+'''
+from .temporary import TemporaryVariable
+from .variable import SlithIRVariable
+
+class TemporaryVariableSSA(TemporaryVariable):
+
+    def __init__(self, temporary):
+        super(TemporaryVariableSSA, self).__init__(temporary.node, temporary.index)
+
+        self._non_ssa_version = temporary
+
+
+    @property
+    def non_ssa_version(self):
+        return self._non_ssa_version
+