Version 4 - Photon + Treemaps ++

[zz85]

This PR prepares for the upcoming release with the following new features and changes

• Treemap Support (Fixes #2). Initially implemented with d3.js, the data binding portion has been modified to first use an invisible and detached svg dom, and now the d3 dom interface have been stubbed for better performance. the rendering portion uses a custom canvas rendering to support potentially thousands to ten thousands of files in the treemap
• Photon Skinning (Fixes #3). Gives a nicer and more consistent UI
• Memory Monitoring - fun stuff but Mac-only right now
• File Scanning RPC has now been switched to run as an invisible Electron Renderer (instead of running in a webview). There's also support to fork scanning as a node process using pipes as communication, but the renderer method is currently preferred
• Level of details viewing - Use +/- to view control amount of depth seen
• Context menu (right click) for deleting (#9), locating and opening files / directories

Pending issues

• [x] Treemaps should keep its navigation path when data updates
• [x] Maintain navigation path switching across Treemap / Sunburst
• [ ] Add transitions for Treemaps
• [x] Modularize treemap/sunburst plugin
• [x] Integrate toolbars with sunburst
• [x] Run filter on (more efficient) treemap walker
• [x] Unify Treemap + Sunburst breadcrumbs (or tidy up the d3 breadcrumbs)
• [x] Context Menus for locating and opening files
• [x] Clean up
• [x] Update README

For future considerations

• Don't regenerate data switching between views?
• Context aware menu (kill/suspend/resume process, open/trash files)
• Remember settings (views/levels etc)

[zz85]

Merging this branch to get a release with Treemaps for early feedback. Treemaps is currently in monchrome without transition animations but should be entirely functional with the exception of minor bugs