DQConnectionPriv: The lastQuery attribute is changed to be a pointer to QSqlQuery
Refactor DQSql - It is no longer an implicitly shared classes.

Changes
 * Changed to explicitly sharing class
 * Added setLastQuery()
 * m_lastQuery attribute become a pointer to QSqlQuery
Added .travis.yml for travis-ci
Added new project : tests/unittests - An unified test project to run every test cases
Deprecate coretests and sqlitetests and moved those code to unittests project
CoreTests and SqliteTests have been integrated with unittests/ project
.travis.yml : Build unittests and run
SqliteTests::datetime() - Added version checking for Qt 5.0.2 and older version