Clarify JSON Procedure with Requirements

Follows @fugu13 's suggestion https://github.com/adlnet/xAPI-Spec/issues/419#issuecomment-25571845
Add optional/required for a number of tables
fixed mbox related links
lower case "object" per https://github.com/adlnet/xAPI-Spec/pull/422#issuecomment-25652244
Required columns on tables From 4.1.4.1 down to 4.1.5
Add missing table heading on Interaction components
Endpoint in example incorrectly included / on the end as well as capital S

Fixed to /statements instead of /Statements/
7.7 Correct capitalization of property in /about resource
Expand acronym on the first use

SCORM was used without expansion.
Also, do we really "need" the copyright symbol on SCORM? Really?
fixes in response to @andyjohnson comments

fixes https://github.com/adlnet/xAPI-Spec/pull/424#discussion_r8100299 , https://github.com/adlnet/xAPI-Spec/pull/424#discussion_r8100339 , https://github.com/adlnet/xAPI-Spec/pull/424#discussion_r8100345
Addresses https://github.com/adlnet/xAPI-Spec/pull/424#discussion_r6925553
All properties on context are optional

Also added some missing </td> tags.
Change yes/no to Required/Optional for attachments
section 4.2 required/optional on tables
section 5.4 required/optional on tables
section 7 required/optional columns on tables
Remove appendices A and B (see https://github.com/adlnet/xAPI-Spec/issues/427)
Fix contents links (https://github.com/adlnet/xAPI-Spec/issues/431)