bug-56: do the followings:

1. add download activity
2. add listadapter for language
3. change wordsstorage to support one db for a lang and category
combination.
4. add dialogutils
5. add errorutils
6. option dialog for partial downloaded db
I found a way can do this shorter: `LayoutInflater.from(context).inflate(R.layout.list_language_row, null);`