Fix incorrect type in some boolean operations on Domain

[btalamini]

The type_ attribute of Domain, which tracks whether the domain is of boundary elements or bulk elements, was not being set for domains created from Boolean operations. The type should have passed from the operands to the created Domain (and the operator should check that both operands have matching type).

This PR does the following:

• adds tests that detect the bug
• removes the default value for the type_ attribute in the constructor, forcing each of the factory functions to explicitly set it
• fixes the bug, and puts in the missing type_ check.

Fixes #1281

[btalamini]

/style