Modules are resolved and variables are replaced

[sbalbach]

• As much as possible from a static scan standpoint, all variables are replaced. To do that, all modules are also resolved.
• Instead of raising exceptions, all failures and errors are stored for use by the caller
• all failures include the problem module and file name
• designed to be used with my fork of terrascan (terrascan-sf until pull request accepted)

[sbalbach]

I can only use python 3.7.3 since all other versions have known vulnerabilities (see here and here).
I have fixed all of the backward compatibility issues that I can. Six tests still fail on older python versions but without being able to step through the code, I cannot find the source of the problems.