bitbake: toaster: Toaster GUI Build and Dashboard pages fixes

bitbake: toaster: Toaster GUI Build and Dashboard pages fixes

THis is a large set of fixes for the generic table, Build and
Dashboard pages.

Among the fixes:
* the table remembers which columns to show across refreshes,
based on saving the settings in a cookie
* added column timespent for a build which is  a denormalization
of the completed_on - started_on information due to limits in
computing datetime differences in the SQL engine
* fixed formatting of the time differences
* various sorting header links fixed
* correct error and warning CSS classes applied to the
respective rows
* fixes multiple divide-by-zero error in displaying duration
estimations

(Bitbake rev: 61e3dee55ac577fce1c0ae0fe7e0d3cf644e8ae6)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>