Reduce code duplication in GSThemeDrawing table/outline view drawing …

…methods (#262)

* Reduce code duplication in drawViewCell:... method

* Further reduce code duplication, add common private method for calculating starting and ending column

* Use the tableView in the method that calculates the starting and ending rows

* Add code to properly handle prototypeViews, the XIB is NOT split, I was confused

* Call awakeFromNib on view as well

* Refactor so that the outlineColumn drawing code is shared

* Adjust the image drawing and the clickable area to be more aligned also make it easier to expand or collapse an item in the outline view