Revert "I removed it->generation, sd->generation, it->walking, sd->walking"

Revert "I removed it->generation, sd->generation, it->walking, sd->walking"

This patch broke at least two stuffs:

1. item movement with key arrow
now up/down arrow scrolls genlist now move to upper/lower item.

2. item del routine.
item del callbacks are called twice LOL.
this also broke apps that use elm_fileselector_button which uses elm_genlist internally.

Once these are fixed and tested more, I will re-commit this.

This reverts commit cea8e755dbf9b062bb1e6d7a89fbf4c590b8f6b3.