Web Enrollment Tweaks

[smcintyre-r7]

This fixes a couple of bugs in the Web Enrollment module that I ran into while testing.

• Fixes the handling of PFX so the datastore option is used, enabling exploitation of ESC2 and ESC3 (tested and confirmed working now)
• Fixes the naming of the AdcsOpts module to be consistent with other files that refer to it as AD CS with a space, making it ad_cs_ and AdCs respectively
• Fixes ESC15 exploitation by moving the ADD_CERT_APP_POLICY option to AdCsOpts
• Improves option validation by moving the checks into AdCsOpts#validate_options, now the other modules get the validation too
• Improves the option handling in CertRequest#create_csr by using #fetch, the caller can explicitly over ride the datastore by setting an option to nil, previously the caller couldn't say for example that there should be no ALT_SID without the method falling back to the datastore
• Improves esc8 UX by setting the Http::Auth option to ntlm by default because it's the only valid setting