Refactor CSS files for podlove-webplayer into SCSS with SASS and Compass

- add Compass config.rb to define paths and the output style for preprocessing css files
- create sass directory for scss files
- create partial scss files for modules, basic settings and components for modularization
- refactor basic styles from old css file into partial files
- import partial files in podlove-web-player.scss
- delete refactored styles from podlove-web-player.css
Move mediaelement styles to partial file and compress lines using scss
Move styles to partial files

- add _theme.scss for specific Podlove styles
- add _button.scss for buttons, _control.scss for controls
- add _utilities.scss for general helper classes like 'hide' 'hidden', 'clearfix',...
- modify other partial files while working in progress (move old styles to partial files)
fix dependency errors

$.url is now required as a module.
embed.init gets the player list as second parameter.
The init function is then called from within the player module after
players are initialised.
Merge branch 'embed' of https://github.com/podlove/podlove-web-player into preprocess-css
Configure debugging statements in config.rb

- Import compass plugin 'sass-css-importer'
- Disable line-comments in css output

Import 'sass-css-importer'
Refactor css

- Import medialement.js into _mediaelement.scss
- Import podlove fonts to podlove-web-player.scss
- Delete _icons.scss and _fonts.scss, they weren't used because of the imports
- Move all theme styles to _theme.scss
Add production css output-file

- Compile to compressed (minified) output css
Update readme file

- Create chapters 'Build CSS', 'Setting up the ruby environment', 'Install SASS', 'Install Compass', 'Build the CSS file'
- Create the chapter 'Contributing' to encourage and help new contributors
Merge pull request #149 from plutonik-a/preprocess-css

Preprocess css
enhance main.js

Do not initialize the embed module for fluent animations.
Add strict pragma.
Remove unused modules
Next step towards general tab registry.

Add tabs module without registry just helper functions.
Extract chapter, downloads and share tab logic.
This is still in progress for chapters at least and will likely be
refactored further.
Merge branch '2.1.x' of github.com:podlove/podlove-web-player into 2.1.x

Merge changed onPlayerEnded event handler manually.
Removed built production file. Remember to rebuild it yourself with:
`browserify main.js -o static/podlove-web-player.js`

Conflicts:
	js/player.js
	static/podlove-web-player.js
update readme.md
SASSes for the masses

Remove built CSS file. So remember to run `compass compile` after
checking out.

Merged from `embed`. Conflicts resulted from some javascript
fixes that were fixed in parallel.

Conflicts:
	js/embed.js
	js/tabs/chapter.js
	main.js
	podlove-web-player/js/player.js
	podlove-web-player/static/podlove-web-player.js
	readme.md