[FEATURE] Implemented Wash mode for the liquify transform tool

There is a fundamental difference between Wash mode and BuildUp mode of
the liquify brush. When you paint on the same place with in BuildUp
(default) mode it adds deformations infinitely, until you hardly see the
original piece. When you use Wash mode, all deformations are limited
by the Amount value, that is they will not exceed this level. You can also
control how fast the deformations will rush to the maximum level by
adjusting 'Flow' parameter, which is available only in this mode.

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