PWA support

[j4k0xb]

Closes #32

To recap:

• Allows installation on PC/Mobile
• Limited offline usage:
  • List of all firmware versions, vendors and hardware targets
  • Lua script download
  • E.g. you previously built firmware 3.5.1 for Happymodel ES24 Pro 2.4GHz TX, it can then be rebuilt offline with a different bind phrase, etc
• Follows the same principle as Change Vite register type to prompt for PWA betaflight/betaflight-configurator#4059 with a reload prompt (when a new version is deployed)

A few suboptimal things, that may be implemented later:

• Better user experience by force-reloading instead of prompting on the main page (no risk of losing data)
• When being offline and fetching anything that isn't cached, it silently fails. Should add a dialog
• Haven't found a way to add the material design font here:
  • https://github.com/j4k0xb/web-flasher/blob/dd3f1f8f4dff4e2b5cd010f9ef1d5c0613049bda/vite.config.js#L14
  • https://github.com/j4k0xb/web-flasher/blob/dd3f1f8f4dff4e2b5cd010f9ef1d5c0613049bda/vite.config.js#L41-L48
    means it's not cached unless you previously visited the hardware selection while being online: