import all Excel sheets to tables

Convert all sheets in a Microsoft Excel (xls or xlsx) file to
geodatabase, dbf or INFO tables. Took the code sample in the "Excel To
Table (Conversion)" help page and turned into an easily reusable script
and tool.

Added parameter for table prefix instead of using the spreadsheet name.
(For instance I want all my Coded Value Domain tables to start with "cv"
instead.)