Add default_layout so we can use it for all forms

[duleorlovic]

Move process_options from helper since we can not override helper.
When someone wants to extend BootstrapForm::FormBuilder and use it in
form_with .... builder: MyFormBuilder, before this change he could not
use in this way since determination whether it is :inline :horizontal
was done in helper.

[bootstrap-ruby-bot]

	1 Warning
⚠️	Please update CHANGELOG.md with a description of your changes. If this PR is not a user-facing change (e.g. just refactoring), you can disregard this.

Here's an example of a CHANGELOG.md entry (place it immediately under the * Your contribution here! line):

* [#550](https://github.com/bootstrap-ruby/bootstrap_form/pull/550): Add `default_layout` so we can use it for all forms - [@duleorlovic](https://github.com/duleorlovic).

Generated by 🚫 Danger

[lcreid]

Good to hear from you again. This is a nice PR. I like your idea. It makes more sense to put the option in the builder itself, rather than the helper.

I don't understand why you had to change the test cases you had to change. If you know why, please let me know. I would think that moving the place where we set the option should require no changes to our tests. If I get some time I'll try to figure it out, unless you answer first.

As soon as we understand why the tests changed, we'll look at merging this PR.

[duleorlovic]

The change in test is only about adding class new_user which rails adds automatically for form_for syntax if html: { class: } were not given in apply_form_for_options (please note reverse_merge and actual source for new_name class).

So I need to change only those tests that were using layout: :inline option for form_for since now we add form-inline in builder (not as html: { class: 'form-inline' } option for form_for).

If you like, I replaced those tests with newer form_with syntax and than we do not have those additional classes. I will revert last commit if form_with syntax is not needed.

I think it is safe to merge since this pull request will only add new_user class for layout: :inline forms (so form will have new_user form-inlne instead of form-inline class) and only for old form_for syntax.

[duleorlovic]

I reverted Use form_with syntax since is it not available on Rails < 5.1...

[lcreid]

Sorry for the slow response. Unfortunately, I don't use this gem in my day job, so it can be a struggle at times to find time to work on it.

I played around with your PR a bit and looked at what it's doing, and I'm pretty much convinced that in fact you've found some tests that were "wrong" by my criteria. I want to do a bit more research to see when the wrong tests were introduced.

Please be patient. I will get to this soon. Thanks again for the contribution.

[lcreid]

I am comfortable that the change in test cases introduced by the PR is in fact the way they should be. If we break any existing users' code (which I think will be in relatively few cases), I'm comfortable defending it as a fix to code that was broken.

@duleorlovic I'll merge this now, but please confirm that we don't need to change any documentation (I don't think so, but please forgive me for double-checking.)

[duleorlovic]

I think example in README is enough https://github.com/bootstrap-ruby/bootstrap_form/pull/550/files#diff-04c6e90faac2675aa89e2176d2eec7d8R624