Changes

Adds use let def strict option to the project properties

The -strict flag was added to VDMJ to address #736.

VDM projects can now use default or strict let def type checking.
This commit adds that option to the Typecheck group in the VDM Settings.

This commit reverts the changes made in 915ddc that used a launch
configuration settings approach.
 (commit: bca2a6a)