[ADD] website_slides: new module doing stuff. I swear.

Courtesy of a lot of people including Mantavya Gajjar(mga-odoo), Ravi Gadhia(rga-odoo),Vijay Patel(vip-odoo), Pariket Trivedi(ptr-odoo)

[REVIEW] Pre-merge review. This commit will have to
be squashed, but not before the end of the review process.

[FIX] broken uploader: for url upload provide image preview

[FIX] broken things after refatoring

[FIX] view count

[FIX] view_count and runbot error

[FIX] small issue related to slide like and most_viewed slides side bar

[FIX] grid view layout

[FIX] side panel layout

[FIX] download and fullscreen

[FIX] suggested slide layout

[FIX] notification mail send

[FIX] channel grid view layout

[FIX] embeded view

[IMP] slide embed pdf viewer

[FIX] embed view: suggested slide layout

[IMP] for like,dislike remove bootstrap alert-dismissable add popover

[FIX] comment route path