Add exec_cached

[ChillerDragon]

The exec command is nice to load configs. But it's not ideal for binds. Because it does read from the disk every time. If it is a frequently pressed bind that is a bunch of unnecessary IO. Also it logs every time and spams the console.

So exec_cached should read a file only once and then store the data in memory. If it is run again it will not print anything to the console.

[ChillerDragon]

Another idea would be to add methods to the config language. Because that is what exec is abused for in those binds. To have multiple commands run at once.