Add support for manifest and modulepath in master section

WIth this patch we should be able to move all specific params concerning git_repo or dynamic_environments to its own classes.

For example:

```puppet
class puppet::profile::git(
  $git_repo_path,
  $git_branch_map,
  $post_hook_content,
  ...
) {
  class { 'puppet':
    manifest => '$confdir/environments/$environment/manifests/site.pp',
    ...
  }
  file { "${puppet::server_git_repo_path}/hooks/${puppet::server_post_hook_name}":
    ...
  }
}
```

 Or even remote it from this module because IMHO it's out of scope. What do you think ?