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
Ok. Got it.

We can do it because this is a callback function which is called when ListView tries to show the row. So, they are run at different timing. But it may introduce some race condition. So, I will move the initialization of storage before initAdapter.