LDEV-1978: Filter access to Learning Flash sequence, in addition to securing single Activity access. This prevents unnecessary ToolSessions from being created.Also, find exact user's ToolSession when accessing Monitor, rather than iterating through them.
LDEV-1978: Check for Lesson's allowed users rather than ToolSession's ones, because an unathorised access to some Tool's Learner creates a separate ToolSession for that singe user (so he is an allowed person).