Fix replay menu loading time by using a cache file

[elexis]

This problem was reported in ticket:3258#comment:15

Problem: If you open the replay menu, it will read all replay files it finds in the sim_log directory.

While the parsing in C++ is quite optimized (only reads the first and last 5 or so lines) and also the JS & GUI handling is fast enough (half a second for 2500 replays), having to open these files the first time can take up to a minute. This is because the files are scattered around on the harddrive and it needs some mechanical work to locate the files.

After that the files are loaded into the HDD cache and this process only takes milliseconds.

Solution: The correct solution to address this disk I/O problem is to have a custom cache file. This way files will be read only once, ever. (Immediately after the game or when opening the menu and finding new files).