Update .gitignore and .keep files

* These directories already exist and have a `.keep` file.
* Follow Rails' convention of `.keep` instead of `.gitkeep`.
* Totally replace `.gitignore` for cleanliness and to allow Suspenders
  to be run with thor's `-G` flag.

Fixes:

#183

lib/suspenders/app_builder.rb

@@ -183,25 +183,19 @@ def setup_stylesheets
     end
 
     def gitignore_files
-      concat_file 'suspenders_gitignore', '.gitignore'
+      remove_file '.gitignore'
+      copy_file 'suspenders_gitignore', '.gitignore'
       [
-        'app/models',
-        'app/assets/images',
         'app/views/pages',
-        'db/migrate',
-        'log',
-        'spec/support',
         'spec/lib',
-        'spec/models',
-        'spec/views',
         'spec/controllers',
         'spec/helpers',
         'spec/support/matchers',
         'spec/support/mixins',
         'spec/support/shared_examples'
       ].each do |dir|
         run "mkdir #{dir}"
-        run "touch #{dir}/.gitkeep"
+        run "touch #{dir}/.keep"
       end
     end
 

templates/suspenders_gitignore

@@ -1,10 +1,16 @@
 !.keep
 *.DS_Store
+*.swo
 *.swp
-.env
+.bundle
+.sass-cache/
 bin/stubs
 coverage/*
+db/*.sqlite3
+db/schema.rb
+log/*
 public/system
 rerun.txt
 tags
-vendor/bundler_gems
+tmp/*
+tmp/**/*