Move gitignore for web build out of package

Mave the ignore entry for packages/master/static out of
packages/master/.gitignore to avoid npm using it and causing the web
build to be excluded from the package.

.gitignore

@@ -45,6 +45,9 @@ static/export
 saves
 /temp/
 
+# Web build
+/packages/master/static
+
 # IDE
 .idea/
 .vs/

packages/master/.gitignore

@@ -1,2 +0,0 @@
-# Webpack output
-static