Add new optional for optional local storage to cache last locale

[John W. Nolette]

v-localize currently assumes it's running in a browser on initialization, and this may not be the case if the given application is using SSR and/or initializing Vue on the server.

I'd like to add an option webStore which will also appropriately check if window is defined.

[John W. Nolette]

Subsequently, stale and hot mode should probably be removed and $locale(...) should return a promise.

[John W. Nolette]

#26