Add preliminary support for Iceshrimp
Iceshrimp (and Sharkey I guess) have the following limitations:
- They don't support the rules API, so registration is broken. This could affect other servers too.
- They don't support the read marker API, so the home timeline never loads.
We can solve these two problems and restore proper Iceshrimp support. Two things to note if you want to test this:
- Iceshrimp doesn't support the registration flow, so you can't register in Tokodon itself.
- Iceshrimp doesn't support oauth codes, so make sure to use the webview or external browser method.
Some of this will be ported to 24.12.