(CSS) fix assets so that they'll precompile cleanly

- fixes 2 typos
- add workaround for CSS files in subdirectories: move the require
  lines to toplevel (application.css) instead of via the @import
  directive in CSS file in the subdirectory.
  (There's a bug in Sass so that @import statements in subdirectories
  don't work properly.  Hopefully that will be fixed in future versions
  of Sass.)
(design) fix big icons for IE

- the reported problem was that these icons were appearing as huge
  in IE9.
- This was because, although there were height and width attributes
  inline on the IMG tags, IE was preferring the width:auto and
  height:auto set in a bootstrap stylesheet (for responsive design).
- It's better to prescale the images this way, anyway.  Save on
  bandwidth, etc.
  (The only reason it wouldn't be better to prescale would be for
  retina-ready images.  But we don't support those so much yet ... )
various text updates to views as per Jason

- login: drop browser warning message
- training main page: adjust text on training page as per Rob
- trainee home: drop intro text for now
  (TODO) add some text back later.
Merge pull request #21 from nmassey/updates

ready for IE (we hope)