[CLEAN]: remove unused variables and change attachment => slide

[FIX] fetch pdf datas only when slide-id found
[IMP]: improve code for to get youtube data
[imp] website_slides: converted extract_youtube_id function to regular expression for get youtube id

[imp] website_slides: Re-converted extract_youtube_id function to regular expression for get youtube id
[IMP]: improve code for model, view and controller
[IMP] add quick propt dialog to create new channel and category

[FIX] FF specific ui issue: send by mail button should be visible in full width

[FIX] broken assets
[FIX]: improve data and demo data
[IMP/ADD] minified build of pdf.js and pdf.worker.js, used closure compiler to generate minifield build, ref: https://github.com/mozilla/pdf.js/wiki/Frequently-Asked-Questions#minified
[imp] website_slides: optimized pdf viewer in embed view after backend corrections
[FIX] Crawler should handle white space in path as like browser does

[IMP] improve backend views

[IMP] Apply PEP8
[imp] website_slides: added promote functionality for slides in slide grid view
[IMP] usability: backend view + add channel setting button in frontend
[IMP]: improve promote button in slide-grid layout
[IMP] Set page titel for channels and set required field based on slide type
[IMP]: small type improvements
[imp] website_slides: optimize image height problem in related slides list in embed view