Include datepicker translations (fixes #167)

This includes all available translations for datepicker (version 1.10.3).
It also contains a list of all available translations in order to check
that the translation exists before including the translation file.
Finally, it puts the <script> for the translation inside the {% compress
%} tag.
Remove {% get_localized_datepicker_js %} from ...

{% compress %} tag to enable offline compression
Add comment to remember why the tag is outside ...

compress.
Remove jquery-ui-i18n.js
Merge branch 'master' of https://github.com/spapas/wagtail into spapas-master