Add csrf token handling

This adds csrf token handling based on a modified version of Rack::Protection.
Add a csrf_token_field helper for forms

The token field is automatically generated without user interaction
Use the master version of rack-protection
Port rack/protection#46 temporarily
Revert "Port rack/protection#46 temporarily"

This reverts commit 7c207aa53cfcc9e119dfe355be6f739f72ceb674.
Remove rack-protection from Gemfile
Add minimum rack-protection version
Merge pull request #1100 from skade/authenticity_token

Add csrf protection through authenticity_token
Merge remote-tracking branch 'upstream/master' into super-admin

* upstream/master:
  Add minimum rack-protection version
  Remove rack-protection from Gemfile
  Revert "Port rack/protection#46 temporarily"
  Port rack/protection#46 temporarily
  Use the master version of rack-protection
  Add a csrf_token_field helper for forms
  Add csrf token handling
  Move rake initialization into CLI
Merge branch 'super-admin' of github.com:WaYdotNET/padrino-framework into super-admin

* 'super-admin' of github.com:WaYdotNET/padrino-framework:
  Refactored the admin generators to support namespaced apps and to read a bit better. Also disabled `-a` since it wasn't really doing anything and left a few notes to implement them. Please, see the conversation at: https://github.com/padrino/padrino-framework/issues/854#issuecomment-14749356 I don't think this should be a blocker to release 0.11.0 and the rest of the admin needs to get there in time!..