give templates a common dot.gitignore

if a template (built-in, downloaded or otherwise) doesn't supply its own
dot.gitignore file then templates/dot.gitignore will be used

also, update dot.gitignore to ignore chains.json by default

lib/utils/template_generator.js

@@ -107,10 +107,8 @@ class TemplateGenerator {
     utils.sed('package.json', '%APP_NAME%', name);
     if (fs.existsSync('dot.gitignore')) {
       fs.moveSync('dot.gitignore', '.gitignore');
-    }
-
-    if (fs.existsSync('dot.gitignore')) {
-      fs.moveSync('dot.gitignore', '.gitignore');
+    } else if (!fs.existsSync('.gitignore')) {
+      fs.copySync(fs.embarkPath('templates/dot.gitignore'), '.gitignore');
     }
 
     if (installPackages) {

templates/demo/dot.gitignore

@@ -1,6 +0,0 @@
-.embark
-config/production/password
-config/livenet/password
-coverage
-dist
-node_modules

templates/dot.gitignore

@@ -1,4 +1,5 @@
 .embark
+chains.json
 config/production/password
 config/livenet/password
 coverage

templates/simple/dot.gitignore

@@ -1,6 +0,0 @@
-.embark
-config/production/password
-config/livenet/password
-coverage
-dist
-node_modules