[IMP] compress *logo*.png with pngquant
[ADD] http.send_file() helper
[IMP] use http.send_file() for /logo.png
[WIP] Testing javascripts in the bottom of the page
[IMP] Move website_sale_tracking.js in front-end bundle
[IMP] Move website_mail_group floating assets in frontend bundle
[ADD] Helper for /website/image (allows to use aggressive cache)
[IMP] Compress resized /website/image's

Refactored and fixed tools.image_resize_image() that converted to RGBA
after making thumbnails, resulting in bad looking picture in case the
source is in 'P' mode (indexed palette)
[IMP] Convert product demo png's to 8bit
[ADD] tools.image_save_for_web() helper for image compression
[ADD] Compress uploaded image by default

Added an opt-out option available from the button's dropdown
[ADD] ir.qweb render_attribute() hook for postprocessing
[ADD] image_save_for_web() format argument
[IMP] add `url_for` hook to bundle urls
[FIX] double html escaping in qweb
[FIX] website.image_url() access rights
[MERGE] Miscellaneous SEO improvments

- Compress images using pngquant
- Added http.send_file() helper
- Move javascripts in the bottom of the page (better google pagespeed ranking)
- Added website.get_image_url() helper that uses a hash allowing the usage of
  a more aggressive cache
- Misc. tools/image improvements
[REM] unused class attribute
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64