audit-logs: ensure nullable FK IDs for mysql

audit-logs: allow showing individual entries for audit log.

user-groups: use request partial renderer and not the pylons one.

logging: use logger_generic in all suitable places, and fix get_current_rhodecode_user() function to use the new mechanics from pyramid. Fixes #5390

user-groups-audit: properly link to user_group when doing api actions of remove and add an user on user group.

user-groups-audit: properly register add/delete members on main edit screen for user group. ref #5390

forms: unified usage of h.secure_form. Make sure we ALWAYS pass in request, and removed redundant 'POST' type.

routing: remove usage of url.current from pylons.

routing: removed more usage of pylons url() objects.

pytest: use ipdb as default --pdb handler