[CStdString] start to demise CStdString

Hi,

This starts to demise CStdString using a function-by-function approach. In this PR I've tackled Format and replaced all occurrences of CStdString.Format with StringUtils::Format.

I'd like to push these in as cosmetics in-between windows, even though they're potentially large scale changes? Maintaining the large number of modified files in these branches through commit windows will be nearly impossible, so I'd like to keep the time between doing the work and committing small. I reckon I can mostly demise CStdString 4-5 days if I can keep pushing the commits in.

Thoughts?