Fix potential intermittent failures related to configuration synchronization
Code clean-up
This commit introduces a new preview property for link content items.

 * `httpsAccessible`: Whether or not a link is available over HTTPS

It also fixes an issue in the embeddable check by passing in a fake
user agent.
Added a testcase that marks http-only URLs as  + some minor cleanup
#748 - minor code cleanup
Overriding the e-mail address during a CSV import if the `forceProfileUpdate` parameter is `true`
Follow-up

 * getOrCreateUser returns a boolean indicating whether or not the user was created
 * Only updating the user during import when there is a diff
#781 - Reverting the publicAlias when possible
Follow up on email address CSV import
#781 - Importing users in a new tenant for each test
Make resource child documents registered externally
(Issue 579) Allow pluggable child documents
(Issue-579) Ensure users, groups, members and memberships are reindexed with reindexAll
(Issue 579) Message search, improve document deletes and one-many parent-child
(Issue 579) Added tests for message search
(Issue 579) Cleaning up use of constants for search document mapping names
(Issue 579) Self-review
Use API method for submitting index tasks, filter by resource type for child producer
(Issue 579) Review followup
Boost query on  field