Add multifile content upload.  This are actually cherrypicked commits from another branch to keep the git history clear.
Merge remote-tracking branch 'origin/master' into feature/contents_upload

# By Andreas Kaiser (4) and others
# Via Andreas Kaiser (1) and others
* origin/master:
  Require kotti_tinymce 0.4b2
  Don't require unreleased versions.
  Require deform_bootstrap 0.2.10.
  Update some requirements' versions.
  Update kotti_tinymce to version 4.0.2.
  Change because of changes in deform_bootstrap
  Change because of changes in deform_bootstrap
  Added css for error validation on tabbed forms.
Merge remote-tracking branch 'Kotti/master' into feature/contents_upload

* Kotti/master:
  Require kotti_tinymce 0.4b3.
Require kotti_tinymce 0.4b4.
Merge remote-tracking branch 'Kotti/master' into feature/contents_upload

# By Daniel Nouri (7) and others
# Via Andreas Kaiser (2) and others
* Kotti/master:
  Require kotti_tinymce>=0.4
  Fix #253: Many translations weren't included in the last release.
  Fix #252: Wrap templates where extract_messages failed with <tal:block>
  Needs to use .prop instead of .attr. Also deleted the unused function variable and changed .is to .checked as it is way faster (http://jsperf.com/prop-vs-ischecked/5).
  How to install a specific release.
  Update version
  Back to dev
  Prepare for release
  Fix #251: Broken comparison of NestedMutationDict and NestedMutationList.
  Require kotti_tinymce 0.4b4.
  Modify few translated strings.
  Modified a translate string.
  Added my signature to CONTRIBUTORS.txt.
  Add french translation.

Conflicts:
	requirements.txt
Split tests.
Add missing test teardowns to doctests.
Restore Image.type_info.addable_to in browser.txt
Remove file that slipped in accidentally.  [ci skip]
Merge pull request #261 from disko/feature/contents_upload

Feature contents_upload