Add progressbar to validator validation

[bilbo]

When I press "Validate", the validation can take sometimes around a minute, if used on very large data set.

There are multiple tests in validator, so when pressing "Validate", a progressbar (perhaps even cancellable progressbar) could be added, so you'll know which test is run currently and you can estimate how long to finish (and so you may also notice which of the test takes so long time, so you can perhaps write patch with some optimized version of it :). This could be done similarly to the progressbar shown while fixing things.

[Gubaer]

fixed in [o17722], plugin is [o17723]