Support sending keys with GnuPG 2.1.
* src/confdialog.c (gpa_configure_keyserver): New. * src/gpa.c (main): Do no get a default keyserver for GnuPG 2.1. * src/options.c (gpa_options_read_settings): Ditto. * src/settingsdlg.c (save_settings): Do not set a default keyserver for GnuPG 2.1 * src/gpaexportserverop.c (confirm_send): Ask to configure keyserver. Support GnuPG 2.1. (send_keys): New. (gpa_export_server_operation_complete_export): Support GnuPG 2.1.