Clean-up code, do minor refactoring of variables

CurrencyListActivity:

 -delete unused amountEntered EditText variable.
 -make the needed variables local.

MainActivity:

 - Make the needed variables local.
 - Move part of the javadoc to the ProgressFragment as it is now
   responsible for that functionality.

SettingsActivity:

 - Make the neede variables local.

ExpensesFragment:

 - Make the neede variables local.
 - Remove unnecessary anymore ACTIVITY_COMING_FROM_KEY String and code
   that pertains to it along with it.
 - Refactor the names of the variables in the prepareListData() method to
   more logical ones.

ProgressFragment:

 - Make the neede variables local.