Content activity
Content screen created

A new activity representing the content screen is now created. In the
next step I'll try to pass data from the main screen to the content
screen. These data are related to the content and the questions of each
level. Then the content and question screen should update accordingly.
Merge branch 'ilias_branch'
String values added

I simply added some string values in the strings.xml file. They
correspond to each level's questions and answers.
*amer, you have to add your own string values
Wrong/right answer dialog boxes
Wrong and Right Answer dialog boxes added

After the user chooses an answer a new alert dialog box is created.
Then a condition statement check if it's wrong or right and leads to
the same or the next question respectively.
Wrong/right answer dialog box (update)
CongratulationsActivity

This activity represents the congratulations screen that appears on
each level after the user answers five questions.
Merge branch 'ilias_branch'
Functionality - Navigation

This commit contains:
a)splash screen
b)a main screen that the user can scroll horizontally between different
levels
c)the content screen that contains the content the user has to learn in
order to answer the questions
d)the question activity
c)the alert dialogs for wrong and right answers

future additions:
congratulations screen
adjust each screen according to the level
Merge branch 'master' of https://github.com/ik23/UCPisFun