Fix for broken forums due to forum entry with no start_date

Switch to using environment variables to get key for Segment.io

Bug fix for LaTeX source not saving

CHANGELOG entry for the whitelistable sandboxing change.

need to comment out another thumbnail check due to build test environmen...

need to comment out another thumbnail check due to build test environment not having libjpeg installed

These CHANGELOGS were never used, and are now obsolete.

css_click will try clicking multiple times.

disable assertions on thumbnail generation as it puts a system requireme...

disable assertions on thumbnail generation as it puts a system requirement on libjpeg which may not be installed on the test machines

Feature/cale/xblock init

Fixes JIRA LMS-203

Feature/cdodge/soft delete assets

allow for an optional throw_on_not_found on contentstore().find() so we can clean up caller logic in the tests