Fixed 'bulk edit' form.

There was an error in 'bulk edit' form (500 when trying to change device's state from 'verified' to 'unverified') - the following pull request fixes it.

Apart from above, it turned out that there are some unused/unnecessary fields on this form as well - this pull request removes them and introduces some cosmetic changes making 'bulk edit' form look more coherent with the rest of UI.