Add separate SetLifetimeStart and SetLifetimeEnd virtual methods.
Add separate SetLifetimeStart and SetLifetimeEnd virtual methods.

SetLifetime is protected instead of public.

peppy/osu-framework,ZLima12/osu-framework,ZLima12/osu-framework,smoogipooo/osu-framework,ppy/osu-framework,peppy/osu-framework,ppy/osu-framework,ppy/osu-framework,peppy/osu-framework,smoogipooo/osu-framework