Bugfix: Keep import path and context for plugin scss imports

 - instead of concating all files into one gigantic file reuse the importer
 - and that way keep the context for relative paths in plugin scss
Changes to posts template to make it easier to display posts on top.
BUGFIX: adjust page padding when composer view open

From https://meta.discourse.org/t/discourse-general-polish/13184 :

"Footer padding gets out of sync: start typing a new topic in the composer ... size it big ... got to random topic ... footer padding is not added so you can not see the last post on topic. (workaround, resize composer once more so footer padding is added). This need to be added everywhere automatically. Including admin screens."
Merge pull request #2254 from bradx3/fix_composer_padding

BUGFIX: adjust page padding when composer view open
Merge pull request #2250 from ligthyear/fix-plugin-scss-import-path

Bugfix: Keep import path and context for plugin's scss imports
Merge pull request #2232 from vikhyat/username-on-top-setting

Add option to show username on top of posts instead of the left gutter
FEATURE: lock icon for archived topics

remove model sniffing hack