Kibana currently stores it's entire application state in the URL by rison encoding it and sticking it into a query string parameter, _a for AppState and _g for GlobalState.

This has functioned fine for a while, but Internet Explorer's short URL length restriction are starting to become a problem for more and more users. To provide these users with a workaround this adds an advanced config option that will store the state in sessionStorage instead of the URL.

This is accomplished by hashing the serialized version of the state, storing a short version of the hash in the URL, and storing the whole serialized state in sessionStorage using the hash + state-type as a key.

Since sessionStorage is limited in size, we must clean up old stored states after they become unreachable to the application. This is done using the new `LazyLruStore` class, a wrapper around sessionStorage. This wrapper helps us maintain the list of stored states based on the time they are accessed (On each set the access time is updates).

It's cleanup style is configured with it's maxItems, idealClearRatio, and maxIdealClearPercent configurations. The defaults for which should be sufficient.

`maxItems`: limits the store to n items, removing the oldest item when the list overflows
`idealClearRatio+maxIdealClearPercent`: when `store.setItem(key, value)` throws an error we try to clear space equal to `idealClearRatio * (key+value).length`, but no more space than `totalSize * maxIdealClearPercent`

…directories.

…move unused '#remove' method.

…ateStorageHash module.

- Replace with HashedItemStore, createStateHash, and isStateHash.
- Refactor stubBrowserStorage.

…reStateInLocalstorage

Rather than enable a behavior we would rather not keep by default, we'll keep it opt-in and link to it so that users who have issues can find the setting