Add essential_matrix_ constructor for rotation of other type

[tom-osika]

Python bindings for essential_matrix were added in 94d1d8336974c0fb793e0ee87c5715b003ecca1c as a part of dev/finish_vital_type_bindings. Because of the inability of pybind to handle templates, templated classes are bound as separate classes on the Python side. essential_matrix_ is templated over floats and doubles, and has a constructor accepting a vital::rotation_ of the same type. It may be convenient to add a constructor accepting a rotation of the other type on the Python side (essential_matrix_<float> can accept a rotation_<double>, etc.) This is similar to #988 #986 and #985