toastergui: changes to the all projects table

toastergui: changes to the all projects table

The 'Last build' column in the all projects table
was supposed to provide the completion time stamp
of the latest project build. Instead, it is showing
the time stamp of the latest project activity, which
includes:

* when the project was created and
* when the last build started

but not when you make a change to the configuration.

The result is that the column and the sorting are very
misleading. The template is set so that the time stamp
only shows when the project has builds (if 0 builds, no
time stamp is shown). But of course the sorting still
happens according to the value, even if it doesn't
display. The result is that, when you sort by the
'Last build' column, projects with no builds
appear listed between projects with builds, and you
have no idea why.

This patch:

* changes the column label
* its position in the table
* makes sure the time stamp always displays
* and adds help text

to reflect what the data actually means.

It also makes some small changes to other table
headings.

Signed-off-by: Belen Barros Pena <belen.barros.pena@intel.com>