Added logout() function

Added a function that logs the designated user out of the system.

Signed-off-by: Sebastian Lenartowicz <slenarto@uoguelph.ca>
String formatting fix in login()

Fixed some string formatting issues in login().

Signed-off-by: Sebastian Lenartowicz <slenarto@uoguelph.ca>
Merge branch 'master' of https://github.com/BlackBox3750/System