Prevent an assembly product to be a part

Currently there's no support for multi-level nesting (i.e. a part that has parts).
Localize :assembly_cannot_be_part error message
Extended gitignore list.
Shorten readme suffix.
Removed Versionfile.
Better readme.
Trim all those whitespace.
Move shared connection to support folder.
Cleanup gemspec.
Namespace locales.
Updated travis.yml

Test it with rvm 1.9.3 and 2.0.0 and notify the irc channel. But there
is not yet no build for
https://travis-ci.org/spree/spree-product-assembly
French locale renamed properly.
Add Swedish locale.
Some changes if it ever gonna run on Travis.
Updated engine.

The most important fix here is the missing newline to add_javascripts.
The rest just follow how new spree engines are generated (with tweak to
Rakefile to make Thor happy).
Fixes markdown typo.
Apply various dev/test tools and configurations.

- Fuubar
- Coveralls and working Travis setup.
- Integrated version style.
Test for locales.
Fixes wild placement of check boxes on products form page.

So we hook them into bottom of admin_product_form_right and add some
styling, remember space reservation for long phrase languages like
German and Finnish.
Use only gemspec for dependencies.