added `keep_caller_id` option
set `keep_caller_id` to 'true' by default
Added functions check_initial_registration and check_initial_call to see account's initial call/registration status from sup
KAZOO-2940: Set limit for media file upload
Markdownify port requests doc.
Merge pull request #563 from Bat-o-matic/KAZOO-3003

Markdownify port requests doc. W00t!
KAZOO-254: start to update docs to support uploading by content-type
KAZOO-254: doc id format change
KAZOO-254: store system notifications in db, start to rework endpoint
to support POST / content-type combo
KAZOO-254: document getting list of templates available in system and account
KAZOO-254: update view for easier listing
KAZOO-254: list summary of system notifications
KAZOO-254: document creating a system notification template, and how to
fetch/create to an account's db
KAZOO-254: fix schema for To addresses
KAZOO-254: create ignore list for cb_simple_authz for endpoints doing
their own auth
KAZOO-254: read in notification, validate notification exists in system
before creating in account
KAZOO-254: finish docs for config, start to doc templates
KAZOO-254: updates and deletes
KAZOO-254: document creating/getting template content
KAZOO-254: store request headers in the context