Adds:
  - schemaUpgrade method which check the fields to add and delete from old schema;

Adds:
  - Add PostgresStorageAdapter.schemaUpgrade spec tests: creates a table,
    simulates the addition of a new field and checks if its present in the database
Chores:
  - ESLint eol-last fix;

…ecessary piece of code

Add:
  - Check the right columns is present before schema upgrade and the new field is not,
    then check if the right columns is present and the new field;
Remove:
  - Piece of code unnecessary because it not need to remove diff columns;

…nd more tests;

…would

return without doing so. Fixed this.

Chore:
  - Allows class with no column to be upgraded;
  - Test for class with no columns being upgraded;

rewriting method schemaUpgrade