New notebooks (#190)

* Moving source files into source directory

* Added advection notebook

* Fixed subplot spacing

* New 3D case notebooks

* New idealized tests

* Update README.md

* Add files via upload

Updated mtn_wave_tests_1km to restore missing graphics.

* first try at held-suarez

* Updated H-S superrotation notebook

* New level placement tool in an interactive note

* Update README.md for new notebooks

* Added link

* Minor updates to notebooks; deleted fv_eta binary.