Do not calculate name alternatives in case of name not found

[DavyLandman]

Right now when a name cannot be found, typepal looks in the current scopes and finds likely candidates. We've found in some profiles that this can be quite some time loss. This lead to an discussion on a recent call, and this issues captures our insights.

we should only run the string similarity code if the user asks for fixes. This means not part of the solve anymore, but as an aux function that someone can run with the scope & tmodel as parameters.

[jurgenvinju]

• In any case it's better to buy store a TModel in a Command, but to recompute it. That improves accuracy if code has changed and speed of it has not (due to the cache on disk).
• There is currently no mechanism for the lazy computation of fixes based on the errors.
  There is a mechanism for computing command quick fixes on demand (lazily) but it doesn't have access to the errors.
• It's best to keep the fixing code near the error detecting code.
• Perhaps we could extend the current fix discovery features with a new option. Note that a lambda would be nice but we can't serialize them yet. So the constructor approach is better.