Reorder files requiring in main script

The main module VBox is defined in the virtualbox/base script.
However it is used in others which define submodules.
Requiring it first fixes a 'NameError: uninitialized constant VBox' when trying to define those submodules.

Here is the full stack:
```
irb(main):005:0> require 'virtualbox-ws'
NameError: uninitialized constant VBox
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/virtualbox-ws-0.0.6/lib/virtualbox/configuration.rb:4:in `<top (required)>'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/require_all-1.3.2/lib/require_all.rb:75:in `require'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/require_all-1.3.2/lib/require_all.rb:75:in `rescue in require_all'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/require_all-1.3.2/lib/require_all.rb:57:in `require_all'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/require_all-1.3.2/lib/require_all.rb:154:in `block in require_rel'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/require_all-1.3.2/lib/require_all.rb:153:in `each'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/require_all-1.3.2/lib/require_all.rb:153:in `require_rel'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/virtualbox-ws-0.0.6/lib/virtualbox-ws.rb:3:in `<top (required)>'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:58:in `require'
  from /home/user/.rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:58:in `require'
  from (irb):5
  from /home/user/.rbenv/versions/2.0.0-p247/bin/irb:12:in `<main>'
```