Make BindException mandatory only when needed.

Several commands have no need for the BindException field.  This was
adding a hassle for the web tier, as it meant that a useless
BindException instance was created and then thrown away.  Made a
function within the abstract command that by default says the field
is required, but it can be overridden to not require it for
commands that don't need it.
Merge pull request #9 from ualerts-org/QueryCommands

Make BindException mandatory only when needed.