RSA Verifier Circuit for OutDID's verifier

This is a fork of the double-bilnd. What we're solely interested in is the RSA Verifier circuit as part of their solution. This fork applies a very lightweight patch over the original repository, namely:

• In rsa.circom, we changed the base_len variable to 408 and 280. This corresponds to the RSA-SHA-256 and RSA-SHA-1 digest variants respectively. The original version supports RSA-SHA-512.
• In rsa.circom, bigint.circom, and fp.circom, we change all imports to circomlib circuits to point to the same copy of circomlib as our main OutDID verifier circuit. This is important because circom doesn't allow the same circuit to be loaded from two separate files, so we need to have one circomlib copy per project.