bitbake: toaster: Small fixes in tasks UI

bitbake: toaster: Small fixes in tasks UI

This commit:

* Fixes an issue with white space when showing the log
in Cached tasks (task details page)

* Formats the no results alert of the "Prebuilt task
could be based on" search in the task details page

* Brings in the task outcome help text to "Prebuilt
task could be based on" table in the task details page,
to the tasks table in the recipe details page, and to
the all tasks page

* Adds the task_color tag to the "Prebuilt task could
be based on" table in the task details page, so that
each task gets the required visual treatment based on
execution

* Makes sure performance information for not executed
tasks shows in the task details page when it exists
(empty tasks often report a short time, for example)

(Bitbake rev: ff46fd6d8db52eeabe8c938c347ce5ba8d328cc1)

Signed-off-by: Belen Barros Pena <belen.barros.pena@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>