Feature request: navigation pane right next to the file pane for markdown files

[eriksdev1]

 * Xed version (3.4.3)
 * Distribution - Mint Faey 6 LMDE

Issue

Suggestion: Can a panel be added right next to the file pane so a markdown file can be rapidly checked (like bookmarks/navigator), especially for headings and subheadings ?

Thanks in advance

[NormPlum]

Is this a duplicate of #125 ?