Backspace shouldn't wrap

[eater]

Describe the bug
When you hold the Backspace key, it would be nice if it just deleted to the beginning of the current line, then stopped (in my opinion). That is the behavior of a form field or spreadsheet field, so it's more what the user may expect.

To Reproduce
Steps to reproduce the behavior:

1. Input several lines.
2. With the cursor on the last line, hold the Backspace key.
3. Observe that everything on the sheet gets deleted.

Expected behavior
Only the current line should get deleted.

Desktop (please complete the following information):

• OS: Ubuntu 18.04
• Version 0.8.0