GenProject: Make plugin able to exclude some files and normalize paths

- Also include it in nancy sample
Types: add defaultArgRS utility function, used for retrieving values from runner state
Runner: reuse FSI sessions again (up to 10 times).  Allow a plugin to override in BeforeReload

- A long-ass comment in the code explains the rational here
- GenProject plugin now only regenerates the project if the timestamp changes on the project file