prevent chapter caption to be shown in overview if <2 chapters exist
Page Thumbnail Candidates

Turn Page#thumbnail, which hard coded page type names, into generic
Page#thumbnail_file/Page#thumbnail_url which are resolved from a list
of thumbnail candidates defined in the page type.

Allow new file types to be provide thumbnail css rules in entry
specific css file.
Use Thumbnail Candidates in Editor

Resolve page thumbnails just like in the server side case.
prune long chapter title in overview
Add missing Internal Links Overview Piktogram
Do not Escape Descriptions in Internal Links
Add `data-theme` Attribute to Outer Wrapper

Required by `pageflow-chart` gem to apply theme class to chart body.
Add `share` CSS Class to Share Navigation Button

Allows themes to hide the button, if share options are not desired.
Player Controls Style Fixes
increase font size in additional info box
Fix play button position
Error Message for Unmatched Upload

Display an error message when a uploaded file cannot be matched to a
file type.
allow 2-line chapter titles in overview
Extract Paperclip Styles for Thumbnails into Config

Allow reuse and modification of generated thumbnails.
Merge pull request #130 from schoetty/overview

change chapter title behavior in overview
Merge pull request #132 from tf/player-control-css-fixes

Player control css fixes
Merge pull request #133 from tf/unmatched-upload

Error Message for Unmatched Upload
Merge pull request #134 from tf/internal-link-escape

Do not Escape Descriptions in Internal Links
Merge pull request #136 from tf/outer-wrapper-data-theme

Add `data-theme` Attribute to Outer Wrapper
Merge pull request #137 from tf/internal-links-piktogram

Add missing Internal Links Overview Piktogram