Estimated delivery date fix, locale fix, non-US merchant support

 * Fix - Add the estimated delivery date (new option the plugin
settings)
 * Fix - Set locale in the fromat expected by Google Trusted Stores
(new option the plugin settings)
 * Tweak - Allow use of non-US Google Trusted Stores JavaScript (new
option the plugin settings)
 * Other tweaks and code styling fixes

see #3
Localization: Change text domain to `wc-google-trusted-stores`; Load text domain; Add .pot file

Closes #1
Add Grunt & .gitignore

* build
* makepot
* wp deploy - if we get listed :)