* Update copyright file.

 - Add additional copyright holders to general files section
 - Add copyright years to general files section
 - Order copyright holder by year
 - Group files sections
 - Sort groups files sections alphanumerically
 - Document copyright holders & licenses for external modules
 - Add license specifications for: Apache-2.0, BSD-2-Clause,
   dxflib-Commercial-License, GPL-2, LGPL-2.1+, QT-Commericial,
   LGPL-2.1 with Digia Qt LGPL Exception 1.1 & GPL-3.
* Remove extra license file for MetaSearch plugin.
* Install libqgis_server.so in libqgis-dev.
* Install schemaExtension.xsd in qgis-server.
* Install contributors.json & developersmap.html in qgis-common.

Author: sebastic