Login and Populating list using Shared Pref-kush

1) Improved Login functionality by adding major field at login and
forcing user to enter username, password and major. Storing Login
session username in shared preferences.

2) List in Overview is populated by retrieving data entered through user
login screen and is showed to current user (current user is not shown in
list).

3) Action bar title of Overview page is set by getting current logged in
user.