bootstrap3 formstyle improvements

Better bootstrap3 formstyles (I hope).

I modified the formstyle_bootstrap3 and added a formstyle_bootstrap3_horizontal to gluon/sqlhtml.py.

They can be tested with welcome application. You can append in the browser ?h=1 to see the
horizontal formstyle.

Do not blindly merge this pull request. Probably it will need to be discussed first.

Does make sense to ship 2 formstyles?
if not, which one?