Add cloud storage "info".

Some folks are using cloud storage with file synchronization.
Add editor for GNU/Linux

AFAIK textedit isn't include in all GNU/Linux distribution.
I add gedit as the GNU/Linux text editor.

I change the order of the configure commands to be the same of
present in the text.
Added objectives to swc-python files-list ipython notebook
Add key points to swc-python file-lists ipython notebook
Added figures for lists, organized list section.
Adding figures for list references.
Improves base on comments about editor for git

I set GNU nano as the recommended editor and change the position
of some information to not duplicate it.
Some changes about editor for git

Make changes suggest by @ahmadia.
Add field names to the database tables

Helps with understanding which data is retrieved by the queries
Add image to illustrate join
Changes after field testing this summer
DOC fix image path in swc-shell

	modified:   _includes/guide-shell/create/lesson.html
	modified:   _includes/guide-shell/filedir/challenges.html
	modified:   _includes/guide-shell/filedir/lesson.html
	modified:   _includes/guide-shell/find/lesson.html
	modified:   _includes/guide-shell/intro/lesson.html
	modified:   _includes/guide-shell/pipefilter/lesson.html
add TOC for README.md
DOC add lost swc-shell images from swcarpentry/guide repo

	new file:   lessons/swc-shell/absolute_path.png
	new file:   lessons/swc-shell/command_shell.svg
	new file:   lessons/swc-shell/decwriter.jpg
	new file:   lessons/swc-shell/direct_shell_usage.png
	new file:   lessons/swc-shell/filedir_challenge.png
	new file:   lessons/swc-shell/find_file_tree.png
	new file:   lessons/swc-shell/google_vs_grep.png
	new file:   lessons/swc-shell/nano.png
	new file:   lessons/swc-shell/nano_quotation.png
	new file:   lessons/swc-shell/permissions_table.png
	new file:   lessons/swc-shell/process_stdin_stdout.png
	new file:   lessons/swc-shell/public_private_keys.png
	new file:   lessons/swc-shell/relative_path.png
	new file:   lessons/swc-shell/remote_shell_usage.png
	new file:   lessons/swc-shell/running_a_process.png
	new file:   lessons/swc-shell/running_wc.png
	new file:   lessons/swc-shell/running_wc_sort.png
	new file:   lessons/swc-shell/running_wc_sort_head.png
	new file:   lessons/swc-shell/shell_as_process.png
	new file:   lessons/swc-shell/shell_on_shell.png
	new file:   lessons/swc-shell/x_for_directories.png
DOC add lost part(intro) to the swc-shell

	modified:   lessons/swc-shell/tutorial.html
Grammar fix in swc-git

Thanks to @ahmadia.
Typo correction

Correct some typos point by @ahmadia.

Note: This commit have been amending.
Spelling and capitalization consistency
DOC update `order` variable in `lesson\swc-shell\tutorial.html`
DOC update lessons' link of index.html