cachedInstance(dir) {
        if (!this._instanceCache[dir]) {
            this._instanceCache[dir] = new Instance(this.ui, this, dir);
        }

        return this._instanceCache[dir];
    }
Gets an instance from cache. Populates cache with new instance if none found

@param {string} dir
@param {Boolean} skipEnvCheck
@method cachedInstance
@private