Add archive directory & update generate-images.sh

1) Provide directory where to store:

    * logos of browsers that are no longer active
    * older logos of browsers that are active

   This shift in scope (from only including the latest version of a
   browser logos to including all versions), was made because of the
   recent demand from the users.

2) Update `generate-images.sh` to reflect the change above mentioned.
Add Yahoo! Axis logo
Move IE 6/7/8 & Safari iOS 6 logos in `archive`
Add old Silk logo
Add old Opera (v10-14) logo
Add old Opera Next (v15) logo
Add Shiira (シイラ) logo
Add Camino logo
Add Arora logo