Updated instructions to help new contributors.

The README should hopefully be more helpful to new contributors now. It
explains how to get started in a step-by-step manner. It's fairly high
level, so it might need some additional details in the future.
Replaced the intro.geometry.mdl file with current result.
Changed "World" to "Scene" and fixed numbers (2000 each)
Changed another instance of "World" to "Scene"
Update visualize_plot.rst
Added a copy of the "Scene" selection image and moved images after descriptions
Interleaved two images with the description to be more clear.
Added a copy of the "Object" selection picture for clarity.
Made it clear that the cube needed to be selected for wire display.
Changed "one" to "want" and moved more pictures after descriptions.
Split the description between the images for clarity.
Add local version of images

There is now a directory in the repo that stores all the images for the
tutorials. All the links in the ReST files have been updated to reflect
this. Previously, the images were only stored remotely to keep the repo
size small, but the new method is likely a better option given that
there are more collaborators now who will need to add/update the images.
Merge branch 'master' of https://github.com/cnlbob/cellblender_tutorials

Conflicts:
	examine_annotate.rst
	visualize_plot.rst

I had to resolve the differences between Bob's changes (typo fixes,
clarifying confusing sections, etc) with my changes to the images
(stored locally now).
Changed html_use_smartypants to False.

This prevents the html builder from converting "typewriter apostrophes"
(U+0027) to "typographic apostrophes" (U+2019). This was an issue if
somebody copy and pasted the reactions (e.g. vol1' + surf1,) on the
website, since neither CellBlender nor MCell parse U+2019 as if it were
U+0027.
Updated warning messages to use ReST directives.

ReST has a special directive for warnings, so I updated the message
about outdated images and apostrophe problems to make use of it.
Set Project Directory (rather than Export)

The old version instructed to click "Export CellBlender Project" instead of "Set CellBlender Project Directory".
Merge https://github.com/cnlbob/cellblender_tutorials

Conflicts:
	getting_started.rst
Test