Cache user information in database

[kylebarlow]

This will save information about cluster users into the same statistics database created in #9. Saving user information will allow enable statistics to be printed, so #10 depends on this issue.

The users table should look something like this:

first_date_joined	last_date_joined	username	project
This is the first date the program found the user in a particular lab	This value can be null if a user is still in a current lab (project), or represents the date they left a project if they switched labs	SGE username	SGE project (lab)