Split document app form into separate modules

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/documents/forms/document_version_forms.py

@@ -0,0 +1,30 @@
+from __future__ import absolute_import, unicode_literals
+
+from django import forms
+from django.utils.translation import ugettext_lazy as _
+
+from ..fields import DocumentVersionField
+
+from .document_forms import DocumentDownloadForm
+
+__all__ = ('DocumentVersionDownloadForm', 'DocumentVersionPreviewForm',)
+
+
+class DocumentVersionDownloadForm(DocumentDownloadForm):
+    preserve_extension = forms.BooleanField(
+        label=_('Preserve extension'), required=False,
+        help_text=_(
+            'Takes the file extension and moves it to the end of the '
+            'filename allowing operating systems that rely on file '
+            'extensions to open the downloaded document version correctly.'
+        )
+    )
+
+
+class DocumentVersionPreviewForm(forms.Form):
+    def __init__(self, *args, **kwargs):
+        document_version = kwargs.pop('instance', None)
+        super(DocumentVersionPreviewForm, self).__init__(*args, **kwargs)
+        self.fields['document_version'].initial = document_version
+
+    document_version = DocumentVersionField()