[lib] Moved passwords and notes in subdirs

This is our new structure

    +-- ~/.pwm
       |
       +-- notes
       |  |
       |  +-- google
       |  |
       |  +-- yahoo
       |
       +-- passwd
          |
          +-- github
          |
          +-- google
          |
          +-- yahoo

This change is not backwards compatible! Early adopters have to migrate
their pwm database.