Improve the email store plugin:

* Allow overwrite of data
* Clean up code
* Improve tests
Merge pull request #212 from eordano/feature/betterEmailPlugin

Improvements to email storage plugin
Add email plugin configuration to the README
Merge pull request #214 from eordano/feature/betterEmailPlugin

Add email plugin configuration to the README
Add key/value storage differentiated by email
Merge pull request #215 from eordano/feature/betterEmailPlugin

Add key/value storage differentiated by email
Fixes testing error
Merge pull request #216 from eordano/feature/betterEmailPlugin

Fixes testing error
Add email templates for copay
Merge pull request #217 from eordano/feature/emailTemplates

Add email templates for copay