cgi: Fix checkbox support (fixes #1008)

cgi: Fix checkbox support (fixes #1008)

There was a change in CGI script regarding checkboxes, however it did
not propagate into templates. Based on the change, the only valid check
was if the variable value was checkbox, but some browsers (at least
Firefox) send on as a default value for input form of type checkbox.

Additionally, the value checkbox looks like typo, because we use checked
as value for checkboxes in admin CGI program, so I updated
cgiGetCheckbox() as well.

To fix the behavior, we have to set VALUE="CHECKED" into every tag in
every templates for all checkboxes - this value will be sent in the
input form, so it will properly match with cgiGetCheckbox() logic now.

In the end, I have found out "Preserve Job History" checkbox from
template was handled as text field, which did not look correct.

Fixes #1008