Redesign "Custom" tab on Section and Catalog Item editing screens

Every category and category item have "Custom" tab, where all custom fields
are displayed. It looked normal in 4.x versions, but since 5.x versions we
have completely different color schemes for edit forms and for grids. I
propose to redesign this page by replacing grid with properly designed edit
form where all custom fields are displayed (no pagination as for now).
Also translatable custom fields currently have translation engine (personal
popup for each field) that doesn't match translation engine for whole form
(central language dropdown on top of the form).
Now, when we have updated kMultiLanguage formatter class in 5.0.3 version we
can surely use it to do all dirty job.