Add support for "getFirst" as indicator to get the first observation.
Add support for procedure descriptions linked to externals (http://) sources, only for DescribeSensor.
Merge branch 'develop' of https://github.com/52North/SOS into develop

* 'develop' of https://github.com/52North/SOS:
  Add contributing section to README.md file
  Update RELEASE-NOTES for 4.1.2
  Update version to 4.1.2
  Update HiberanteFeatureQueryHandlerTest to extend from HibernateTestCase.
  Typo
  Fix issue when transactional is supported but a procedure has not validProcedureTime entry.
  Fix invalid time in JSON-InsertObservation example
  set version to 4.1.2-SNAPSHOT
  Correcting version numbers
  Trying to make the fix more general than present use case.
  fixes 52North/SOS#149
  Increase version number.
MySQL/MariaDB datasource for custom mappings

installer is usable if 'MySQL/MariaDB Custom Mapping' is chosen
Merge pull request #157 from autermann/feature/custom-mysql-datasource

MySQL/MariaDB data source for custom mappings
Update RELEASE-NOTES
Merge pull request #158 from CarstenHollmann/feature/sensordescription_from_url

Feature/sensordescription from url