[kernel] move Db functions to Async

src/kernel_services/plugin_entry_points/async.ml

src/kernel_services/plugin_entry_points/async.mli

src/kernel_services/plugin_entry_points/db.ml

src/kernel_services/plugin_entry_points/db.mli

src/libraries/utils/command.ml

src/libraries/utils/command.mli

src/libraries/utils/task.ml

src/plugins/eva/engine/iterator.ml

src/plugins/from/from_compute.ml

src/plugins/gui/analyses_manager.ml

src/plugins/gui/design.ml

src/plugins/gui/gtk_helper.ml

src/plugins/impact/compute_impact.ml

src/plugins/occurrence/register.ml

src/plugins/pdg/build.ml

src/plugins/postdominators/compute.ml

src/plugins/server/main.ml

src/plugins/server/main.mli

src/plugins/wp/Conditions.ml

src/plugins/wp/wp_parameters.ml