Offline-use of icons

[rtpt-romankarwacik]

Is your feature request related to a problem? Please describe.
We usually use gowitness in a browser without access to the internet, which results in the icons for the metadata not being loaded without changing the code:
https://github.com/sensepost/gowitness/blob/master/web/api/wappalyzer.go#L9

Describe the solution you'd like
Maybe adding a flag for the report server to serve the icons directory from a local directory, or even auto-pull the repository itself.