Glimpse v2 - Code Based API for Configuration

We'd like to support users who want to configure Glimpse via a strongly typed code-based API. This would not *replace* the current `web.config` based approach - but would rather augment it.

Here are a few goals for the design:
- [x] `web.config` settings "win". Meaning if there are conflicting settings in the code API and `web.config`, the later will take precedence. This will allow a user to change a setting for Glimpse without recompiling, which is an important use case for a diagnostics framework. *(See [my comment below](https://github.com/Glimpse/Glimpse/pull/504#issuecomment-32483526) to see how this goal has actually shaken out in the wash.)*
- [x] At some point (probably after initialization), Glimpse configuration (or a subset of it) will become immutable. There are just "too many bad things" that can happen by changing configuration while live multi-threaded requests are coming in and I'd rather not have to solve those problems.
- [x] If possible, I'd still like to support IOC based configuration. Glimpse's current implementation, while well meaning, is weak - but most users already have an IOC container they use to resolve their web framework's run time components (controllers, formatters, modules, etc.).