Add elbow-less minimal decision tree

[tsalo]

Closes #1129. I'll actually test it soon.

Changes proposed in this pull request:

• Create a decision tree based on the minimal decision tree, with elbow nodes cut out.

[handwerkerd]

Thank you!
This should also include a figure in included_decision_trees.rst (I can help make the figure) and an update to "[tedana] What are the differences between the tedana_orig, meica, and minimal decision trees?" in faq.rst. Hopefully we can have some people test & make sure this is useful before making those changes.