Fix problem with the drop speed not increasing over time.

The drop speed is not increasing with time.  

In the `AddScore` function, the `dropRate` variable is being decremented, which is used to set the timeout. 

In the `GetNextBlock` function, the `dropRate` variable is being reset to 1000. I am guessing this is to counteract the user drop command, which is setting `dropRate` to 10.

To fix this I have introduced a variable `hardDropping` which is checked against in the `DropBlock` function to get the needed drop rate.