Work around RefError: resort to leaving machineCount empty

Previously, a RefError was triggered, because a text ("1")
was assigned to the machineCount TextField, triggering
onTextChanged before the functions (notably, validateInputs())
were initialized.
Now, there is no initial text assigned.
Fix input validation bug

A case in which machine count was 0 was not
handled correctly.
Implement results-based grid initialization

Grid is now created based on the number of machines
(vertical block count) and on the max job duration per machine
(horizontal block count).
Implement job description drawing