Faster script and better history management

[ipitio]

This PR brings significant (and I mean significant) performance improvements to the script. Also a few QOL fixes and additions.

Sister PRs:

• https://github.com/arevindh/AdminLTE/pull/83
• https://github.com/arevindh/pi-hole/pull/69

Features:

• Delete db backup on uninstall
• Allow restoring db after flushing it while no new speedtests have been run
• A better readme

Fixes:

• Flushing db (#146)
• (Unnecessarily) Getting local AdminLTE version (#150)

Enhancements:

• Compatibility: Removed case fallthrough
• Performance: Prefer git fetch and git reset over cloning or copying directories
• Performance: Always clone with depth=1
• Performance: Uninstall iff installed
• Functionality: Delete empty db on uninstall
• General: Formatting

[town3r]

Excited for this to be fully pushed out. It's been a hot minute since I had this installed. Excited to give it a go again.