add option: hide mask only if value is empty (without mouse events)

[nemiro]

add new option to allow show mask only if user has started input.
mask will not be visibile if value is empty and will be visible if value is not empty.

duplicate of #1302

I will make pull request to latest version.

also I made plnkr, so you can see result by yourself.

example is for 4.0.4 version
see /*inemiro::*/ comment at the inputmask.js
https://embed.plnkr.co/32Yhomx5eyhs1IJus5Xj/

[nemiro]

made new pull to latest HEAD version
#2065

[RobinHerbots]

@nemiro ,

Isn't this the same option as clearMaskOnLostFocus

[PelElMejor]

When I use clearMaskOnLostFocus option, woks, but the mask be show and I need that the mask just be show when I use the input.