add modal dialog & dynamic form to Batch Actions

thanks to @chrise86 for the updated CSS so this isn't horribly ugly
add docs

+ rename from `modalDialog` to `modal_dialog`
+ use the default confirm message on the form if none given
update batch action translations
Merge pull request #1815 from seanlinsley/1815-batch-action-forms

Batch Action forms
small docs update
replaced `eval` with alternatives using `define_method`
replace *_eval with *_exec
Merge pull request #2144 from seanlinsley/eval-is-evil

Stop using `eval`
updates it translations
Merge pull request #2730 from AlessioRocco/it-translations

updates it translations
#2722: has_many CSS fix

scope the relative fieldset positioning to the has_many form so the
login form doesn't break