Organize snippets in tree

Example GitHub provider

• Github
  • maraf
    • Money
      • Issues
      • Pulls
      • Find file
    • certbot-arm
      • ...
  • Neptuo
    • Framework
      • ...
    • Productivity.SnippetManager
      • ...

Searching logic

• Use depth-first search
• Show all ancestors on line that are between selected root and current node
• Tokenize input (split by space or "")
• Transition to next level is on token basis
• Don't include ancestors when all search text is matched
  • Searching for "Money" shouldn't include "issues", "pulls", etc

Example results

• "g" "ma" "re"
  • Github - maraf - aspnetcore
• "g" "re"
  • Github - maraf - aspnetcore
  • Github - Neptuo - Recollections
• "mo"
  • Github - maraf - Money
  • Web Money
• "mo" "iss"
  • Github - maraf - Money - issues
• "iss"
  • First X issues under Github repo

New features

• Use "^" to search from root
• Respect quoted text

TODO

• Create tree based on "name path". Drop generated ids. Allow to nest inline/xml snippets under github node
• Show appropriate portion of title in search results
• Re-allow GitHub org repositories

Closes #47
Closes #34