STORM-593 FIXED Make transparent texteditor and lineeditor

Reason: If some child of transparent LLFloater has a visible non-transparent background then this part of floater is non-transparent. As a result floater became partially transparent.

Solution: When transparent floater changes focus, iterate through its children and set corresponding (corresponding to whether control in active or in inactive floater see STORM-535) transparency value.

- Added method LLUICtrl::getCurrentTransparency. This method calculates transparency level of a control. Calculated value should be used as an alpha chennel value in case we want this control to be transparent. For now this method is used by LLFloater to adjust transparency of its children.

- Added calculating of transparecny level for: LLLineEditor, LLTextBase, LLinventoryListItem, LLScrollContainer, LLScrollListCtrl, LLAccrodionCtrlTab.

- Added method LLFlaoter::updateChildrenTransparency which updates transparency value of its children