add option to turn off mod signature verification

Many of our customers implement Spotfire Server(together with services) environment inside intranet and there is not internet access.

So they also have to change "Require valid signature to allow trust" to false to allow end users to utilize mods signed by a third party(e.g. mods published by TIBCO community).

Every time end users open an analysis with mod in it, Spotfire still tries to verify the signature and it would fail due to lack of internet access, this process takes about 10 seconds, which makes the progress of opening analysis much longer than necessary.

Please add an option to turn off mod signature verification, so that analysis can open immediately, without the delay of the always failing signature verification.