"what(): stoi" error reading TI

[cultpenguin]

When a training image file is not properly formatted mps_* may stop with the error:
"
what(): stoi"
"
This can happen if the first line does not contain number, or of the third line (containing the number of columns) contains a tab/white space after the number.

The code should be more robust to whitespace and tabs, and should provide better error messages for a badly formatted training image file.