Rudimentary calendar/username password saving added

GUI now has a calendar that shows assignments due, however its pretty
buggy and needs a ton more work before its really going to be useful.
Also, a client's username and password are stored so they only need to
be entered at once. Passwords are stored in plain text on android
internal storage, and even though internal storage isn't accessable by
other apps/users, plain text is still a bad idea. Shouldn't be too hard
to implement an encrypted output stream, though.