Ignore files from showing up in a release (#5111)

* moved email css files to template directory
* prevent developer files from showing up in a release

.gitattributes

@@ -0,0 +1,18 @@
+.docker export-ignore
+.github export-ignore
+assets export-ignore
+tests export-ignore
+.codecov.yml export-ignore
+.editorconfig export-ignore
+.eslintrc.js export-ignore
+.gitattributes export-ignore
+.gitignore export-ignore
+php-cs-fixer.dist.php export-ignore
+babel.config.js export-ignore
+package.json export-ignore
+php-cs-fixer.sh export-ignore
+phpstan.neon export-ignore
+phpstan.sh export-ignore
+phpunit.xml.dist export-ignore
+webpack.config.js export-ignore
+yarn.lock export-ignore