Add random change to script transaction

[digorithm]

Full context and discussion here: #89.

The overall idea is to enable contracts calls that may be view-only to be able to be called multiple times without causing tx id collision.

This will be a temporary workaround for the lack of explicit view-only ABI methods and different ways of calling different types of functions (.call(), .send(), etc, as you see in Solidity).

Later, we should explore other potential solutions.