Require simplecov before metasploit_data_models required

[#47896995]

When `rake spec` was run, the coverage reported was 0 / 0 because
simplecov was being required after all the unfiltered paths, such as
app/models/* were already loaded, which means Coverage.result would
ignore those files.  Rubymine did not have an issue because Run with
Coverage starts simplecov before rake spec starts, so the late simplecov
require in spec_helper.rb had no negative effect for coverage numbers in
Rubymine's Coverage Report.
Merges #13, adds spec coverage for Mdm::Modules

Still needs a coverage report to work on the CLI, though.