A lot of template improvements

- Translate group name in participant overview table.
- Move 'status_link' function from participants.js to utils.js for using in VoteCollector plugin.
- Added hook 'post_js' for VoteCollector plugin.
- Fixed poll id in poll_form.
- Improved 'show log' button
- Used welcome_title for default custom slide
- Used bootstraps' fluid grid nesting for responsive layout of widgets.
- Added microphone icon for 'add-me-to-list-of-speakers' button.
- Format motion identifier and title in (motion and account) widgets.
- Format list of speakers (slide, overlay, view, overview)
- Format list of speakers widget and view. Added view to link to current list of speakers (without add to list).
- Fixed motion slide. Made up/down animation faster and the scroll way shorter.
- Fixed icon name.
- Set default context of 'extra_javascript' to use kwargs['context']['extra_javascript'].append('...') without error.
- Fixed translation of motion state.