Feat/generator render widgets

[lissavxo]

Related to #426

Description

Created a new field in the generator.html to select whether it will render a paybutton or a paybutton-widget.

This change will help testing, before generator only rendered buttons now it can be used to widgets too.

Test plan

Run yarn dev access http://localhost:10001/paybutton-generator.html test generating widgets/buttons.

[chedieck]

One thing to notice: this branch has commits from #435, but not all of them (is out-of-date)

When including changes from another branch in the PR branch, try to use the Depends on in the PR description template. This way is easier for reviewers to know which changes to ignore, or which branch to diff it against, or even for you to remember to merge that branch back into this in case that changes (as happened now)