CSP 1.1: Clarify "element's contents" intent.

This block describes the value of "element's contents" for both script
and non-script elements. Adding the words "non-script" and "style"
explicitly to make things clear. Brief discussion in [1].

[1]:
http://lists.w3.org/Archives/Public/public-webappsec/2013Dec/0071.html
CSP 1.1: Clean up 'nonce-value' and hash algorithm.

This patch adds 'nonce-value' back to the grammar, and adds base64
encoding to the hashing algorithm, cleaning up the breakage that
both omissions introduced.

Patch submitted via [1].

[1]: http://lists.w3.org/Archives/Public/public-webappsec/2013Dec/0056.html
CSP 1.1: Denormify the hash mismatch warning.

We don't really want to have normative requirements for things like
console messages. Changing the SHOULD to a non-normative note.