demo: add an EditText control in puzzle view

IMPORTANT:

This is just a demo, trying to give you a taste about my idea.

The reason I write this is because I have a `pgn` file which contains 5335 puzzles,
it is extremely hard to navigate through these puzzles using the `SeekBar` plus sometimes
I accidentally touch the `SeekBar` then I need to spend about 5 minutes to navigate back to 
the puzzle I'm working on.

I'm not familiar with java and android, so there are many things
needed to tweak, for instance:

1, The program will crash if the user enters anything except a
number into EditText.

2, The program should either give a Toast or AltertDialog when
the user enters a puzzle number which does not exist.

3, the layout need to be done by someone who is really familiar
with Android

4, Maybe remove the SeekBar? change it to a ProgressBar?
Sometimes I accidentally touch the SeekBar and will jump to another
puzzle.