Render columns and sections in Rich Text Editor instead of as wiki markup

When a page has been formatted into columns, these are not rendered in the Rich Text Editor. The RTE should render columns and also allow column editing.

1) RTE UI needs a Columns button that launches a popup window. The popup has parameters for

• Column border (default: none)
• Column width in either pixels or percentages (default: unset)
• Add Column button
• Close button
• Space to render up to 8 selectable bars/images corresponding to columns. If the cursor is outside a section, no bars are displayed and the text 'No columns' is shown. If the popup was called while the cursor was inside a section, or a new column was just added, display a selectable bar for each column in that section. If the user selects one of the column bars, that column's border and width are displayed plus new buttons to Update or Delete that column.

2) Render Columns in the RTE as rendered in the Preview tab.