twill tests

Merge branch 'hw8-twill-tests' of https://github.com/ctb/cse491-serverz into hw8

Added cse491.env to GitHub now that it has twill and everything installed.

Used newly-added command-line args parsing to direct server.py to imageapp and
altdemo in order to test pre-written twill tests.

Wrote additional twill test "myapp-1.twill" to test my WSGI app, including the
form submission that then says "Hello Mr. [firstname] [lastname]".
JPEG and TIFF functionality

Modified imageapp so JPEG and TIFF files can be uploaded.

Note: TIFF files DO NOT WORK on Google Chrome and Firefox, but do work on
Internet Explorer.  Wikipedia says that "TIFF has not had a major update since
1992", so I suspect that it is a relatively outdated file format, and Chrome
and Firefox don't feel like supporting it any more.
Final Homework 8 Housekeeping

Changed the text on imageapp upload page to indicate that JPEGs and TIFFs can
now be uploaded in addition to PNGs

Updated ChangeLog