[#832] Remove "jump to modules" link except on mobility

Fixes #832
Merge pull request #845 from afuna/remove-module-jump-link-bug-832

[#832] Remove "jump to modules" link except on mobility
[#836] Use the latest rendering engine available

So that IE is aware of media queries

Fixes #836
[#834] Background color to comments in some layouts

This makes sure that the comment text is readable once they extend over
to the right, and away from the page background

In some cases, add a little padding around the comments so that they
have some space to breathe when they're over the page background

Removes padding from #primary .inner, but adds it back via other
elements, so that there's not doubled padding around comments that are
still over #primary
Merge pull request #849 from afuna/comment-bgcolor-bug-834

[#834] Background color to comments in some layouts
Merge pull request #847 from afuna/turn-off-ie-compatibility-mode-bug-836

[#836] Use the latest rendering engine available
[#837] Use LJ::CleanHTML to process formatted_mail for usertags

Fixes #837
Merge pull request #854 from afuna/format-mail-@username-bug-837

[#837] Use LJ::CleanHTML to process formatted_mail for usertags
[#838] Use generate_medium_media_query instead of $*desktop_media_query

Fixes #838
Merge pull request #863 from afuna/generate_medium_media_query-bug-838

[#838] Use generate_medium_media_query instead of $*desktop_media_query
[#841] Enforce max-width on images in smaller screens

* also removes similar code in some layouts because it's no longer
  needed

* add height to poll image style attribute  so it overrides height: auto
  (but don't remove height attribute, needed for, e.g., email
  notifications)

Fixes #841
[#841] Force a max-width onto embedded content (iframes)

* adds two new wrappers to the generated lj_embedcontent HTML:
  .lj_embedcontent-wrapper and .lj_embedcontent-ratio

* .lj_embedcontent now has a width: 100%, which forces it to be as wide
  as its containing element

* .lj_embedcontent-ratio gives back the height at the original aspect
  ratio using padding-top (we know the given width/height so we can
  generate this dynamically)

* .lj_embedcontent-wrapper forces a max-width/max-height, so that it
  can't go bigger than it was originally defined, or bigger than
  system-limited width/height

* the generated content inside the iframe (embedcontent.bml) is given a
  width/height: 100%, so that it's as wide / high as we defined the
  outer iframe to be

Fixes #841
[#841] Add back image size limits on larger screens

only for Snakes and Boxes, and Trifecta -- this was the old behavior so
let's not change it
[#841] Add image handling to all dw-free layouts

(These are the layouts that override Page::print_default_stylesheets, so
they didn't get the change automatically)

Fixes #841.
Merge pull request #846 from afuna/too-large-media-bug-841

Handle large media (images, iframes)
[#841] Initialize large_media_query variable
Merge pull request #864 from afuna/add-missing-variable-bug-841

[#841] Initialize large_media_query variable
Merge branch 'release-1.21' into develop

* release-1.21:
  [#841] Initialize large_media_query variable
  [#841] Add image handling to all dw-free layouts
  [#841] Add back image size limits on larger screens
  [#841] Force a max-width onto embedded content (iframes)
  [#841] Enforce max-width on images in smaller screens
  [#838] Use generate_medium_media_query instead of $*desktop_media_query
  [#837] Use LJ::CleanHTML to process formatted_mail for usertags
  [#834] Background color to comments in some layouts
  [#836] Use the latest rendering engine available
  [#832] Remove "jump to modules" link except on mobility