Design/Whiteboards/Navigation center

Summary
Implement a single center for all navigation-related commands.

Relevant Bugs

 * Search for "Navigator"

Personas

 * Drew: Reviews long documents with tens to hundreds of pages for a living. He often needs to search for certain terms, filter his results, check on their context, and replace them. He needs to be able to do this quickly and easily.

Description
By default, the navigation center would be a sidebar docked to the right, though it could be docked to the left or made into a floating box, just like the Navigator today. Up at the top of the navigation center would be a search box. Below it is a toolbar with the "Show Replace Box" button on the left and three selection buttons on the right. Clicking the "Show replace box" button shows an entry box with a "Replace" button on the right of it (this button contains a symbol, not a text label). The selection buttons are "All", "Previous", and "Next", in that order. These button work just like the current selection buttons in the "Find and Replace" dialog. If enabled, the Result pane shows up below these three buttons. There is a toolbar at the bottom of the result pane if it's appropriate. A "Show Result Pane" button, the category drop-down menu, and an "Options" menu line the bottom of the navigation center.

Categories
Instead of using the "Content view" to filter out categories, the user is presented with a simple drop-down menu of categories to choose from. These categories include "All content", all the object types (taken from the current Navigator: Headings, Tables, Text frames, etc.) used within the active document, "Spelling/Grammar errors", and then all the styles used within the document (this would replace the "Search for styles" feature). "All content" would be the default category.

Each category has its own view in the result pane. "All content" shows numbered thumbnails of all the pages within a document (or all the slides within a presentation, or the sheets and "data clusters" in Calc). "Headings" lists all the headings and subheadings. This category has a toolbar at the bottom, with buttons for "Promote level", "Demote level", "Promote chapter", "Demote chapter", and "Heading levels shown >". "Tables", "Graphics", "Text frames", and "OLE objects" all show numbered thumbnails of the respective objects in the document. If an object has a custom title, it is shown below the thumbnail. "Spelling/Grammar errors" shows snippets of sentences in which LibreOffice found a spelling or grammar mistake.

Options
The Options menu sports a gear icon and carries the following items:
 * Format...
 * Attributes...
 * Similarity Search...
 * Match Case
 * Whole Words Only
 * Include Notes (only when notes are present)
 * Regular Expressions
 * Drag mode>
 * Drag mode>
 * Drag mode>

Quick navigation
Entering "#" and a number in the search box takes one to the result of that number if it exists (e.g. "#3" under the "All content" category brings one to the third page), but also offers to search for the string "#3" with a "Did you mean to search for "#3"?" link up at the top of the Result pane.

Relevant Art

 * Word's Navigation Pane (this one I found out about when the concept was finalized, yet I'm surprised by the similarities)