Move time related code into canvas_time gem

fixes CNVS-10748

Change-Id: If9015c54bf54969d8c47e5e39a372e1c5bfe158b
Reviewed-on: https://gerrit.instructure.com/32532
Reviewed-by: Raphael Weiner <instructure@pivotallabs.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>
QA-Review: August Thornton <august@instructure.com>