Fixes #107 - Update `build` task for don`t repeat templates

Change  `ngtemplates` in `Gruntfile.js` for replace (not add in the end of file) template.

Removed `ngtemplatesOptions.append` because by default is false and it's necesary for not duplicate templates
If this (and others like it) could be changed back to the way they were before that would be great. We want to make sure that a user could swap out the template at any time so it needs to be the same for bootstrap and vanilla...

Actually, maybe this is a good opportunity to make some changes. How hard do you think it would be to make this url be: `formly-fields/email.html` instead? We're hoping to have other template bases in the future and doing this would make creating a template base much easier to do. What do you think?