Tweak the caching layer

[ralphtheninja]

Currently we have several caches spread out on all the backends, e.g. http and hyper. This code should be moved up one layer, into storage/index.js. This would:

• remove redundant code
• have one point where the caches reside for easier maintenance when clearing cache etc
• enable/disable caching, some endpoints on some platforms might not need any caching, since they are already cached themselves or the indexdb caching is just slower than not using it (I'm looking at you electron + hyperdrive!)
• indexdb is slow and we might need to tweak or replace it and we don't want to do that in several places, also we might use something else entirely in electron (maybe level for node is just fine)

[ralphtheninja]

It would also be easier to add an additional hot cache, where we store frequently requested tree files in memory as well. And once a tree file becomes "old", we clear it from the in memory cache.