add postgre support

pom.xml

src/main/java/com/ic/er/Attribute.java

src/main/java/com/ic/er/ER.java

src/main/java/com/ic/er/Entity.java

src/main/java/com/ic/er/LayoutInfo.java

src/main/java/com/ic/er/Relationship.java

src/main/java/com/ic/er/View.java

src/main/java/com/ic/er/common/Utils.java

src/main/java/com/ic/er/entity/RelationshipDO.java

src/main/resources/jdbc-postgre.properties

src/main/resources/mybatis-config-postgre.xml

src/main/resources/mybatis-config.xml

src/test/java/com/ic/er/TestAttribute.java

src/test/java/com/ic/er/TestCommon.java

src/test/java/com/ic/er/TestER.java

src/test/java/com/ic/er/TestEntity.java

src/test/java/com/ic/er/TestRelationship.java

src/test/java/com/ic/er/TestView.java

src/test/java/com/ic/er/mapper/attributeMapperTest.java

src/test/java/com/ic/er/mapper/entityMapperTest.java