Keep track of mod updates

[paoloambrosio]

Closes #92.

• Use file hash to detect updates
  • Store installed hash
    • After installation
    • From modification timestamp and size
    • Optional for backward- (not present) and forward- (different name) compatibility
  • Read but not store available hash
• Show out of date mods in the UI
  • Add out of date icon
  • Use out-of-date information from mod hash (available vs installed)

Out of scope for this:

• Two-level hash with hash of modification timestamp and size of files (consider file order) Store content hash (from modification timestamp and size of files) for both available and installed mod
  • File hash only for available to know if the content hash has changed since last checked
  • Only for installed mods
  • Store after installation and if changed on fetch
• Versioned (split hasher and hash algorithm with name) (no need for this as the hash would change if different and we would consider it changed even between different hash versions)