Add DeserializeOrigin to LLVMOrigin rewriter

[Drevanoorschot]

This pull request adds a rewriter that transforms DeserializeOrigin to LLVMOrigin.

An issue right now is that i think the type checker is ran before any rewriter is. This means by the time type check errors are reported, the DeserializeOrigin is used which is not very descriptive.

I'm not sure if and how this could be fixed.

[Drevanoorschot]

I corrected the style and naming issues. Regarding the aforementioned type check issue: Perhaps it would be possible to make ColLLVMParser invoke the DeserializeLLVMOrigin rewriter? It would make sure the origins are converted before any error could be raised.

[Drevanoorschot]

I first need to make some changes in VCLLVM before i can test whether the changes work as intended (which will take time), but at least it compiles. Seeing how this PR has been open for a while, it might be best to merge it now before the merge conflicts get complicated to solve. But that call is for @niomaster to make.

[pieter-bos]

Sure, but please address the review comments:

• There are still many formatting changes in Origin.scala in the diff, please back them out;
• the key member of DeserializeOriginToLLVMOrigin shoud be short, and should start with a lowercase letter.