add .distignore for automatic deployment control (#146)

The deployment action utilizes "git archive" if no .distignore is
specified. Doing so, the minified JS/CSS resources are ignored, because
.gitattributes is processed for excludes, but the generated files are
not actually part of git and thus won't become part of the archive.

Using explicit .distignore list we now separate git / Compsoer excludes
from WP deployment. This triggers simple "rsync" without git logic.

.distignore

@@ -0,0 +1,20 @@
+# Directories
+/.git
+/.github
+/.wordpress-org
+/node_modules
+/vendor
+
+# Files
+/.distignore
+/.eslintrc.json
+/.gitattributes
+/.gitignore
+/.stylelintrc.json
+/.travis.yml
+/composer.json
+/package.json
+/package-lock.json
+/composer.lock
+/phpcs.xml
+/README.md

.gitattributes

@@ -8,6 +8,7 @@
 /vendor export-ignore
 
 # Files
+/.distignore export-ignore
 /.eslintrc.json export-ignore
 /.gitattributes export-ignore
 /.gitignore export-ignore