Fixes #5926 - hide sensitive parameter values

User can check to hide value when creating or editing global parameter.
The value is masked by *** and is also not displayed when overriding.

This is meant as short-term solution. Long-term we should move to smart variables and smart class parameters and add proper password support there. I know that similar patch would be handy for smart variables and smart class parameters, but it seems too much work which would be dropped later.
I don't see an easy way, two options I see:
* use ERB so we'd have hidden_values.js.erb, first pass would generate field template here and we'd have to modify some specific attributes like id, name and such but I'm not sure how assets precompilation would work and it seems hackish
* we could create a new helper for hidden values that would generate 2 fields beforehand, one of them hidden, when checkbox is clicked, they'd have to be swapped, modifying their id, name and such which gets a bit trickier because id must remain unique so 3 changes would be needed

while second seems to be feasible, I don't see big benefit since this only happens when switching hidden flag, which I believe happens once per parameter life