Added Story Mode and updated widget_test.dart

• Changed some functionality of the existing game:
  1. Removed option to choose the length of the word.
  2. Length of the word does not affect the number of attempts
• Added story mode
• Updated the widget_test.dart to automate the testing.

requested review from @a.sadriddinzoda

assigned to @a.meslmani

approved this merge request

mentioned in commit 612d1253

merged