add tests for the 'seller' role.

NOTICE: Programmers are REQUIRED to REVIEW AND SOLVE bugs listed in
<seller_bug_report_v3.0.docx> and <seller_bug_tracking_v3.0.xlsx>.

This test suite examines the 'seller' role. Included are the following
3 files:

	Tests/Week_7/Hu_Shaojie/seller_bug_report_v3.0.docx
	Tests/Week_7/Hu_Shaojie/seller_bug_tracking_v3.0.xlsx
	Tests/Week_7/Hu_Shaojie/seller_test_suite_v3.0.xlsx

The contents of these files are:

<seller_bug_report_v3.0.docx>: This document lists all the 9 bugs detected
			       so far in the 'seller' module. It describes
			       the location as well as symptom of each bug.
<seller_bug_tracking_v3.0.xlsx>: This table briefly lists all bugs that
				 <seller_bug_report_v3.0.docx> mentions. It
				 REQUIRES ALL PROGRAMMERS to solve bugs of
				 their code, and after that, FILL IN the
				 'RESOLUTION' and 'STATUS' columns.
<seller_test_suite_v3.0.xlsx>: This test suite lists all the test cases we
			       employed in testing the 'seller' module.
			       Programmers are encouraged (but not necessary)
			       to take a look at this table.

Thank you!
							Hu Shaojie
							Nov 2nd, 2014