Added "if exists" functionality to Template and used to to allow for override js and css files. They do not have to be present, but if they are they are included after math4.css and math4.js and allow a way to override standard theme stuff.
Adding the main color elements to math4-overrides.css.dist
Merge branch 'develop' of https://github.com/openwebwork/webwork2 into css-refactor
This commit does a fair amount
- I added a subroutine to ContentGenerator which allows templates to check
  if a file exists
- I added distribution versions of untracked "override" files for math4.css
  and math4.js.  When missing they will be ignored, when present they will
  allow people to override the math4 css and js in a way that is not tracked
  by git.
- I added an "alternative coloration" of math4 to show how this can be done
  in a way that keeps track of changes from upstream.
- I added some comments and other things to make it a little more obvious
  how to set site_info.txt in such a way as to be independant of switching
  branches
- I deleted some unused theme files.
tweaked green theme
Polishing
More polish.
Final polish
Deleted extra thing.
Fixed gitignore bug
Reverting .gitignore change
Now there is a file (math4-coloring.css) which is tracked by git and will be
added to system.template when it is present.  This can be used to create
colored themes that will be distributed via git.
Fixed achievement progress bar coloring.
Merge branch 'develop' of https://github.com/openwebwork/webwork2 into css-refactor
Fixed a harmless js bug in math4 when using gateway.template.
creation of a red theme
Merge pull request #4 from pstaabp/testing/css-refactor

creation of a red theme
Cleaned up red theme a little and added hover color
changed back some of the standard colors for warnings/alerts/etc.
Fixed missing coloring css for gateways.