Added Oracle synonym's support

Implemented support of oracle synonyms. Now they can be created and deletedby this way:
```xml
<changeSet id="Create synonym new_synonym" author="Ivan">
	<ora:createSynonym objectName="object" synonymName="new_synonym" />
</changeSet>
<changeSet id="Drop synonym new_synonym" author="Ivan">
	<ora:dropSynonym synonymName="new_synonym" />
</changeSet>
```