remove secrect_token from

version control, this should not be checked in
rake task for generate secret_token

- adapt session secret rake task for rails3
- added secret_token.rb to .gitignore
better handling of secret_token

- deafult value in test / dev env
- possible to set it with env variable
- rake task to generate secret_token
- fixed ci task for travis
exit with error if secret_token ist empty
Merge pull request #156 from opf/feature/rails3_fix_secret_token

Better secret token handling