Missing OSGI exports in flowable-engine-common

**Describe the bug**
The module flowable-engine-common is missing the following OSGI exports:
- org.flowable.common.db.mapping
- org.flowable.common.db.mapping.entity

Because of those missing exports, mybatis won't be able to load some files in an OSGI environment and will lauch the following error:

`org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource org/flowable/common/db/mapping/entity/Property.xml`

**Expected behavior**
Add the missing exports in flowable-engine-common pom.xml under section .