Ability to customize caption block used on all forms in administrative console

Currently each form control in administrative console is composed from 3 parts:

• caption part - field name, required mark, additional icons (e.g. open fckeditor)
• data part - input control (textarea, radio buttons etc.)
• error part - code, that displays field validation error

There are separate block for each type of control. I propose to make "caption part" of each "inp_edit_*" block customizable via specifying alternative caption block. For now we could use this advancement to unify "inp_edit_textarea" block.