Add configurationProperties on MybatisProperties

[kazuki43zoo]

I've added configurationProperties on MybatisProperties for customizing a global property.

mybatis-config.xml:

<properties>
    <property name="key" value="value1" />
</properties>

Can override a defined property or define a new property at application.properties as follows:

mybatis.configuration-properties.key=value2

These properties can use as placeholder(${...} format) in mybatis-config.xml and SQL statement. (In this case, ${key} will replace to value2)

Please review.