Provides read access to tool parameters, which are (name, value) pairs.
Write access is not allowed. This provides
an unmodifiable Map that looks first in the tool configuration, then in
the tool registration, then in the servlet configuration. The values
in the tool configuration may have been configured by the end-user,
the values in the tool registration are defaulted in the tool registration
file, and the values in the servlet configuration come from web.xml and
cannot be modified by the user.