Fix for sketches script usage in checker options

Reduced blocking timeouts in the UI to 250ms and full block to 5000ms.

Fix for nested lambda tooltips not showing if they were generic
functions.

Refactored some common symbol parsing code so it can be reused rather
than copied.
Why not just use "fsscript" as your sketch indicator, or use some commment in the file (e.g. "// sketch" as the first line) ? The F# langauge spec says that scripts end with fsc/fsscript - it is a shame to introduce a new extension which will only work with your sketches tooling.