Improved strict mode support

- Tested with latest mobx and mobx-utils
- Tested against `{ enforceActions: "always" }` a.k.a. very strict mode
- Added `getNonReactive` method, a convenient way for unit tests to access the most recent value outside of a reactive context
- Looks like `Reaction` in `mobx` has changed slightly so can no longer support `throttledComputed` synchronously throwing outside reactive contexts; removed a couple of tests for that.

.gitignore

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 node_modules
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+.DS_Store