CA-141389 Log all GET and POST calls

Some paths were already logged in HTTPHelpers.cs, but other paths weren't. I have added logging for the missing ones, except for stats gathering for the performance graphs and search page, which are called too often.

Unfortunately, we don't always have the full URL until we get into HTTP.cs, but that's in the public SDK so the only way to add logs there would be to pass in a logging delegate, and that would break backward compatibility of the SDK (or cause us to carry two copies of every function). I decided that it wasn't that important.