Handle 404 and 500 errors

Use custom handler for 404 and 500 errors
Redirect to #404 and #500 so that pages are rendered correctly,
and backbone can display appropriate error templates
Merge branch 'master' into issue#345_404
Merge branch 'issue#345_404' of git://github.com/sujeetsr/rockstor-core into sujeetsr-issue#345_404
Modified template and html files
Merge branch 'issue#345_404' of git://github.com/sujeetsr/rockstor-core into sujeetsr-issue#345_404
Add 404 and 500 views to views/__init__
Merge branch 'issue#345_404' of git://github.com/sujeetsr/rockstor-core into sujeetsr-issue#345_404
Added 404 and 500 views
Merge branch 'issue#345_404' of git://github.com/sujeetsr/rockstor-core into sujeetsr-issue#345_404
Handle 404 and 500 errors

Add global error handler for ajax error
Add global error message template
Remove cutom 404 adn 500 django handler view
Modify 404.html and 500.html
Merge branch 'master' into issue#345_404
Modifications to handle ajax errors globally
Merge branch 'master' into issue#345_404
Merge branch 'issue#345_404' of git://github.com/sujeetsr/rockstor-core into sujeetsr-issue#345_404
Merge branch 'master' into sujeetsr-issue#345_404
Client side error handling

Add common error template for errors
Display error message detail if present, otherwise unknown error message
Add appropriate messaging for the user to contact rockstor for help
Merge branch 'issue#345_404' of git://github.com/sujeetsr/rockstor-core into sujeetsr-issue#345_404
Client side error handling

Remove error message handling from individual views
Merge branch 'issue#345_404' of git://github.com/sujeetsr/rockstor-core into sujeetsr-issue#345_404
Modify 404 and 500 templates to match front end messaging