First pass at converting "blame" commits into a unified model

Since we are using native date formatting the formatter abstraction is no longer needed

Adds new visited paths trie for fast lookup of seen paths (to avoid git calls)
Replaces the tracked cache with a paths trie
All tries are case aware based on os and scheme (if uri based)

Adds new detectNestedRepositories setting to improve performance
Automatically handles nested repos for open document and remaps paths
Reworks isTracked for perf & nested repo detection

Changes excludes to a Set for faster matching
Splits getRepository into get & create (also removes async for get)
Replaces repo path methods with repo versions (part of moving away from string paths)
Renames getRemotes to getRemotesWithProviders & getRemotesCore to getRemotes

Should help with eventual testing

Abstracts node path imports to system/path

Reorganizes local git support to exclude from web
Swaps sha1 usages to md5 to avoid needing sha1 on the web (md5 is required by Gravatar)
Avoids crypto-browserfy and imports md5.js directly
Uses platform crypto for random nonce strings

Adds proper reveal to repo folders
Adds reveal to contributors git commands

Actual paging will have to be implemented later

This is to ultimately will support virtual repositories (without git)

Uses new quick pick buttons api

Adds advanced.externalDiffTool setting
Adds advanced.externalDirectoryDiffTool setting

If repo lacks watching, pretend change checks are true if unknown change

Adds a deny everywhere option
Adds command to reset denials