Refactor deployment

This should fix #373

 * Use rbenv
 * Fixes for Centos

I didn't overly test the development deploy.

Wiki documentation would need to be updated slightly.

```
{

"name" : "huginn_production",

"chef_type" : "role",

"json_class" : "Chef::Role",

"description" : "Huginn Production Environment",

"default_attributes" : {
  "mysql": {
    "server_root_password": "password",
    "server_repl_password": "",
    "server_debian_password": ""
  },
    "nginx" : {
       "init_style" : "upstart"
    }
},

"run_list":[
             "recipe[git]",
             "recipe[apt]",
             "recipe[mysql::server]",
             "recipe[nodejs::install_from_binary]",
             "recipe[nginx]",
             "recipe[ruby_build]",
             "recipe[rbenv]",
             "recipe[huginn::ruby]",
             "recipe[huginn::user]",
             "recipe[huginn::production]"
           ]
}
```

The roles now share most of the code for setup, with only the ```huginn::production``` and ```huginn::development``` recipes differing.

You can now pick your own attributes, like ruby version, git repo, etc:

```
default['rbenv']['ruby_version'] = "2.1.2"
default['rbenv']['plugins'] = [{
  'name' => 'rbenv-sudo',
  'git_url' => 'git://github.com/dcarley/rbenv-sudo.git'
}]

default['huginn']['repo'] = "https://github.com/cantino/huginn.git"
default['huginn']['branch'] = "master"
default['huginn']['rails_env'] = "production"
default['huginn']['keep_releases'] = 5
default['huginn']['user'] = "huginn"
default['huginn']['group'] = "huginn"
default['huginn']['deploy_path'] = "/home/#{node['huginn']['user']}"
default['huginn']['env']['invitation_code'] = "try-huginn-secretly"
```

Mail details still probably need refactoring.
Yeah, I've let the underlying system work out which package manager to use and just assumed it is present. Given the small number of libraries with minor name differences, spitting out two lists seemed easiest.