Improve package structure [DATAJDBC-138]

[spring-projects-issues]

Jens Schauder opened DATAJDBC-138 and commented

• move SimpleJdbcRepository in support package
• move the mapping package in the core package
• rename JdbcEntityTemplate to JdbcAggregateTemplate

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Referenced from: pull request #67

[spring-projects-issues]

Jens Schauder commented

Since this is based on your feedback from last year and since you have similar cleanup stuff in the pipeline I'd appreciate if you could take a look at this one