Bumping version to 4.2.
Compute button spacing delta via intrinsicContentSize

Avoids potentially triggering recursion by inspecting a subview.
Merge pull request #1931 from wordpress-mobile/issues/1926-autolayout-crash

Compute button spacing delta via intrinsicContentSize
Remove slicing data from btn-primary-tap asset

We're slicing in code anyway, and it was crashing for some reason

Fixes #1946