display error if train process crashes

[lolo8304]

Describe the bug
due to error in regexp the training was crashing ... in the frontend, the state is still "training" and never changes the state

To Reproduce
Steps to reproduce the behavior:

1. Go to 'entity regexp'
2. enter wrong regexp
3. update
4. train
5. See error in console

Expected behavior
show error message or status change in training status box (top right corner). I know this should never happen, but during alpha, beta or future test stages it would be good to have it.

Screenshots
described above

Desktop (please complete the following information):

• OS: mac
• Browser chrome
• Version 70.x

Additional context
also checkout issue
#15