First commit for 404 (etc) error pages.
Merge pull request #86 from yeastgenome/system-pages

First commit for 404 (etc) error pages.
Added cytoscape download button.
Refactoring network and tables and writing tests.
Finished writing basic tests.
Merge branch 'sequence-fixes' into refactoring-templates

Conflicts:
	src/sgd/frontend/yeastgenome/static/templates/sequence_details.jinja2
Merge branch 'master' into refactoring-templates
Merge branch 'refactoring-templates' into sequence-fixes
Fixed #2845.