Cache vuex store

[robbevp]

Description

Fix #39
This uses the same idea as #48 but with a few differences.

Different caches

We store data in two places: localStorage and localForage. localStorage is prefered since it is synchronous, so it is used for most modules. This way we have instant access to data from those modules

The main collections that are to big to be stored inside localStorage and are stored in localForage.
I've added a subclass to VuexPersistence that allows us to save and restore data in a memory safe way. (VuexPersist would try and merge the existing store with the savedStore, which would cause huge spikes in memory usage), we can now use the mutations within each module.

Router isn't blocked

I've placed the await store.restored before we would commit something in any of the modules that are stored async. Since we overwrite the way this value is set, we have a separate restored for each module that is stored async.

This way we can already render the page while data is loaded from localForage. A user might experience a 2-3 sec delay before the page is populated with data, but that feels very acceptable.

Filter mutations

Just as in #414. We only set a cache when something inside of the modules in the cache is changed.
This makes that commits in the player don't have any effect on the cache.

Debounced saveState

The methods that are stored in localForage have their saveState wrapped in a debounce with a wait time of a minute.
If a user is editing, loading data, it doesn't make much sense to save the state after every mutation. Since we don't use these values directly, the user should not notice this.
(There is a slim chance that the user closes the tab before the data was stored, but if that is the case, the user will get the updated data soon after loading the app.)

How Has This Been Tested?

Tested by refreshing quite a bit during the course of a day in both Chrome and FF.

The usual memory usage might spike up to 200MB when restoring or saveing the cache from localForage and settled to around 80MB - 120MB after this.

[robbevp]

I've also created a PR with vuex-persist: championswimmer/vuex-persist#218
With this change we can cache tracks without too much of a performance hit

[chvp]

Seems more correct to me. Feel free to disagree.

[chvp]

Sorry, didn't see the merge conflicts before approving.

[robbevp]

@chvp rebased