added section matlab gui

* added section about matlab gui elements
* added paragraph about matlab documentary
lesson 1 update

* fixed typos
* moved workspace section
* removed “current “folder”
update lesson 1

* added paragraph to ensure everyone’s setting the path at the start of
the lesson
update lesson 1

* word wrap
* moved current dir paragraph
Merge pull request #794 from IsaKiko/novice_matlab_lesson1_review

Added some notes on the MATLAB GUI and setting the working directory.
update lesson 2

* fixed some minor issues
* short paragraph on commenting
changed list numbering back
typo
avoiding i as an index in MATLAB materials

* replaced ‘i’ with ‘idx’ in lesson 2
* replaced ‘i’ with ‘j’ in lesson 4
i --> idx
Merge pull request #799 from ashwinsrnth/matlab-05-defensive

Matlab lesson on defensive programming
Merge pull request #821 from ashwinsrnth/add-next-steps

Add next steps