Detect unsupported platforms

Detect unsupported platforms and try to help the user, if there is
something they can do about it.

For example, not every JRuby mode is unsupported, we can guide the user
what to do to enable support for that platform.
Store and check an unique session id when evaluating commands

This will avoid CSRF attacks to execute arbritary ruby code using the
console.
Release 2.0.0.beta4
Merge pull request #52 from gsamokovarov/unsupported-platforms

Detect unsupported platforms
Refactor DOM rendering and copy/paste support
Merge pull request #53 from ryandao/copy_paste

Refactor DOM rendering and copy/paste support
Don't keep Gemfile.lock in version control
Drop the Dockerfile

Thanks for it @StanAngeloff. It was really useful during our testing.
Let escapeHTML be more paranoid
Avoid monkey patching ActionController::Base#initialize

Just inverting a condition does it.