Maybe get rid of lscache dependency

[srabraham]

Currently our client code relies on four external dependencies: Bootstrap, DataTables, jQuery, lscache. lscache hasn't seen any updates in 3 years, and is a lesser known package.

I like severing dependencies wherever possible, and especially so in frontend code (as I mentioned in another issue recently, these are dependencies on the internet that we have while on-playa). We only made simple use of that lscache dependency in the first place (get and set), and I was able to write the below replacement very easily. I'd like to just replace the use of that external dependency with this code.

function storeLocal(key, value, ttlSeconds) {
    localStorage.setItem(`ims.${key}`, JSON.stringify(value));
    localStorage.setItem(`ims.${key}.deadline`, `${Date.now()+ttlSeconds*1000}`);
}

function retrieveLocal(key) {
    const val = localStorage.getItem(`ims.${key}`);
    const deadline = localStorage.getItem(`ims.${key}.deadline`);
    if (val == null || !deadline) {
        return null;
    }
    if (Date.now() > new Date(Number.parseInt(deadline))) {
        return null;
    }
    return JSON.parse(val);
}