<data-source> in persistence.xml

[gavinking]

This changeset realizes the idea proposed in #864, namely, that it should be possible to declare and configure a DataSource in the persistence xml file.

For example:

    <data-source name="jdbc/library">
        <description>My example persistence datasource</description>
        <class-name>org.postgresql.Driver</class-name>
        <url>jdbc:postgresql://localhost/library</url>
        <user>gavin</user>
        <password>p0ny</password>
        <isolation-level>TRANSACTION_READ_COMMITTED</isolation-level>
        <max-pool-size>100</max-pool-size>
        <max-idle-time>10000</max-idle-time>
    </data-source>

Or:

    <persistence-unit name="Library" transaction-type="JTA">
        <description>My example persistence unit</description>
        <data-source>
            <description>My example persistence datasource</description>
            <class-name>org.postgresql.Driver</class-name>
            <url>jdbc:postgresql://localhost/library</url>
            <user>gavin</user>
            <password>p0ny</password>
            <isolation-level>TRANSACTION_READ_COMMITTED</isolation-level>
            <max-pool-size>100</max-pool-size>
            <max-idle-time>10000</max-idle-time>
        </data-source>
        <class>org.example.Book</class>
        <class>org.example.Author</class>
        <class>org.example.Publisher</class>
        <exclude-unlisted-classes/>
        <shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode>
    </persistence-unit>