Vanilla score test

[ekatsevi]

This pull request includes the following new features:

• There is a new argument in set_analysis_parameters called response_regression_method, which can take values approximate_nb (what we were doing previously) and nb (a new option involving running an NB response regression). The print() function now displays the response regression method.
• The argument resampling_approximation now has the option standard_normal, which bypasses any resampling and instead compares the test statistic to N(0,1). Note that this option requires response_regression_method = "nb". This functionality is accompanied by the test named "run_calibration_check with score test".
• The option resampling_mechanism = "crt" is now available for ondisc-backed sceptre objects.

[ekatsevi]

A few other notes:

• Checking the package examples takes upwards of 20 minutes, with check() reporting about 20 or so functions whose examples require more than five seconds. I don't know if this is a problem.
• Rebuilding the vignette appears to takes a while as well; I skipped it when checking the package.
• I removed the package R.utils from the sceptre dependencies, because apparently sceptre no longer depends on this package.