Added package user, classes AbstractUser, MainUser and Friend

method getAsParseObject shouldn't work yet.

	new file:   WordFinder/src/ch/unibe/scg/team3/user/AbstractUser.java
	new file:   WordFinder/src/ch/unibe/scg/team3/user/Friend.java
	new file:   WordFinder/src/ch/unibe/scg/team3/user/MainUser.java