Add constructor for mocks

[grongor]

These changes will simplify the tests by not being required to assert mocks expectations every time. This will also eliminate situations where your tests are not failing even though they should, only to find out that you forget the defer statement.

Example
Before:

factory := &mocks.Factory{}
defer factory.AssertExpectations()

something := &mocks.Something{}
defer something.AssertExpectations()

something.On("GetTime").Return("tooLate")

factory.On("Create").Return(something)

testThings(factory)

Now:

factory := mocks.NewFactory()
something := mocks.NewSomething()

something.On("GetTime").Return("tooLate")

factory.On("Create").Return(something)

testThings(factory)

These changes are based on a branch where I did some refactoring, you can see it here #399. If you don't intend to merge the refactoring PR, I can rebase this branch onto the master.

[grongor]

Closing this to re-open immediately to run on the new GitHub CI

[grongor]

New PR here #406