Merge branch 'develop' into qt5_port

.gitlab-ci.yml

CHANGELOG.txt

CMakeLists.txt

cmake_support/FindSQLite3.cmake

docker/Dockerfile

modules/conop/src/compound_lib.cc

modules/conop/src/compound_lib.hh

modules/db/src/CMakeLists.txt

modules/db/src/sqlite3.c

modules/db/src/sqlite3.h

modules/db/src/sqlite_conv.hh

modules/db/src/sqlite_wrap.hh

modules/doc/install.rst

singularity/Singularity.1.9.0