add RVM support

1. change `bundler` task to not use `--deployment` when using RVM
2. add task to create RVM alias and wrappers for `application` so it's easy to use it in scripting / cron

to activate RVM support:

```ruby
set :rvm_type, :system
set :rvm_ruby_string, "1.9.3@#{application}"
set :rvm_require_role, :rvm
require "rvm/capistrano"
```

use `:app` for `:rvm_require_role` if all `:app` servers should use RVM

cron support:

```bash
application="my-app-name-from-deploy.rb"
PATH=/usr/local/rvm/wrappers/${application}
```

conditional scripts:
```bash
application="my-app-name-from-deploy.rb"
rvm_path=/usr/local/rvm
if [[ -s "$rvm_path/environments/${application}" ]]
then PATH="$rvm_path/wrappers/${application}:$PATH"
fi
```

this is work in progress:
- `gem install rvm-capistrano -v ">=1.3.0.rc11"`
- https://github.com/wayneeseguin/rvm-capistrano/blob/feature/readme_for_1.3.0/README.md