Drush aliases for automatically created multisites

[becw]

Addresses #105.

• Creates a drush aliases file in drush/ when installing the-build
• Adds a new alias to the drush alias file when creating a new multisite
• Adds the multisite config to the-build's properties file automatically

To test:

1. Install the-build with vendor/bin/the-build-installer
2. Run drush sa -- it should list a sitename.local alias for your site
3. Create a new multisite with phing drupal-add-multisite
4. Run drush sa again -- there should be a new sitename.local.NEWSITE alias for your new multisite
5. Also, your .the-build/build.default.properties.yml file should have the Drupal sites configuration for your new multisite

A couple notes...

• This code got super messy because whitespace within XML is awkward

[becw]

Merging so that I can cut a new alpha tag.