Relayout Problems view

Made Problems view easier to use, especially when viewing problems and coding at the same time

* Moved tasks to a partial, and moved them to be part of problem description
* Fixed floating terminal in responsive mode (no more overlap when in single column)
* Made entire problem container fixed height (height of window on load)
* Make footer dark
* Make some important/commonly used buttons primary
* Convert SCSS to SASS files (will continue to do this as I work on stylesheets. SASS has no curly braces or semicolons FTW!)

TODO
* Make tasks tabbed for easy browsing, one tab per task with solved/wrong solution indicator on tab itself
* Test IE8 compatibility
* Determine nav and footer height dynamically when setting problem container height
* Resize fixed height of problem container when resized (probably add window resize listener and bind value to inline style). Feel free to attempt this.


@yihangho, would appreciate your code review for this to make sure I didn't break anything. Only worked on view and stylesheet files, so hopefully should be OK. Thanks!