Add support for per-mock strictness

[thevoiceless]

See mockito/mockito#1272

Mockito 2.20.1 added support for per-mock/stubbing strictness. It looks like the most straightforward option would be passing an additional argument to withSettings().

[thevoiceless]

For anyone wanting to use this in the meantime: You simply replace whenever with Mockito.lenient().`when`, or Mockito.mock(Foo::class.java, withSettings().lenient()) to make the entire mock lenient.

[thevoiceless]

Actually, it looks like this may have been fixed 10 days ago with #353

It allows passing the lenient parameter to mock(...) but does not add a lenient version of whenever