Fixed two issues and refactored extension name (#788)
Composer fixes.

- Use DIRECTORY_SEPARATOR to check bolt's path so that it works on all
  platforms.
- Update Bolt\Composer\ScriptHandler\isntallAssets() - app.php no longer
  exists and attempting to copy it causes an error.
Fixed typo in contenttypes.yml.dist
Merge pull request #790 from bacbos/extension-MenuEditor-1.4.2

Fixed two issues and refactored extension name (#788)
Merge pull request #791 from solarissmoke/composer-fixes

Composer fixes.
Merge pull request #792 from tchebb/patch-1

Fixed typo in contenttypes.yml.dist
Bumping version to 1.4.0.
Tweaking ImportWXR -> added menu-option, set requirement for 'developer'.