I also added license information to source files where it was
missing and changed the way the license block is organized. All
the sources' license information comments follow the same pattern:

/* [ Optional short file description ]
 *
 * [ Optional copyright notices]
 *
 * License information block
 *
 * [ Optional 'Authors:' section ]
 */

The LGPL is references consistently now; source files with main()
function, like tests or D-Bus services, use 'program' in the license
information block, while the other sources use 'library' word.