Use nbsp in checkbox label if empty

To keep the label tag from having a 0 height (causing the checkbox to be mispositioned), some text needs to be in the label. This uses a nonbreaking space when checkbox_label is set to 'label'. See #898.
Added support framework.validation.transaltion_domain parameter
remove size attribute in time widget

this attribute seems to be useless and because of it, the height of time selects are inconsistent
[FIX] Font-awesome path for less
Fix DOM element removal in order to be compatible with IE8

According to javascript documentation it seems that the element.remove() method does not exist
Btn-default for form button by default

Regarding the [Bootstrap docs](http://getbootstrap.com/css/#buttons), button with no extra class must have `btn-default` with the `btn` class.
fixed mirroring
Choice widget expanded "inline-btn" for bootstrap buttons http://getbootstrap.com/javascript/#buttons-examples
Update fields.html.twig
Merge pull request #943 from piotrantosik/master

fix non exist array keys
In datetime_widget in 'datetimepicker' mode, display date if it has value
use block "form_widget_simple" to avoid code duplication
Merge pull request #944 from AppVentus/master

In datetime_widget in 'datetimepicker' mode, display date if it has value
Merge pull request #938 from Soullivaneuh/patch-1

Btn-default for form button by default
Merge pull request #937 from jfacchini/fix-collections-js-ie8

Fix DOM element removal in order to be compatible with IE8
Merge branch 'master' of github.com:benbor/MopaBootstrapBundle into benbor-master
Merge branch 'benbor-master'
This should do the trick.. Fixes #906
Merge branch 'MisatoTremor-collection-addremove-config'
Merge pull request #905 from MisatoTremor/fix-collections

Fixed the custom LESS and SASS for collection-item