Merge search inputs into one, add spell drop overlays as POIs

[WUOTE]

I believe these should be addressed simultaneously:

1. There is a request from the wiki people:

is there a way to link to a specific spell overlay? I'll add something to the spell infobox

2. Having a second search box just for spells is confusing, so I'd like to see them merged into one. As for how to fix two different behaviors when selecting a POI, and a spell: selecting a spell in the search results -- the “go to the POI” should frame all the overlays that are active + toggle overlays.

[ashleybaldock]

I suggest making the variable part of the inbound links be just the Spell ID (if possible), as it makes it easy to include links to them from other tools - you only need to know the base URL and ID to generate a link. (All the spell wiki pages implement this via a redirect from their ID, e.g. https://noita.wiki.gg/wiki/MANA_REDUCE -> https://noita.wiki.gg/wiki/Add_Mana)