Default plugins

# New Feature: Default plugins

Option to create a configuration file of default plugins to be installed with every new site. 

Create a new line plugins.conf for each plugin you would like to install at the creation of a new site. Each line will be parsed and installed using WP-CLI

Other Changes:

New Variable: VVVSWDIR - /Path/to/directory/for/vvv-site-wizard. Currently used to find the plugins.conf file.

Converted large printf statement used to create vvv-init.sh into heredoc for readability.