Handler test prevents invalid chars from removing textbox

This is the same behavior as of MUI1. Also Windows uses 530 ms by default.

The implementation is somewhat dirty, but I can't think of better way.
I renamed constant E to NAPIER, as it clashes with E notation. I don't think someone will use this anyway.

Printing to log might make people think it's bug in code.
This feature can be used for indicator of what's wrong with the use input.
This also stops function construction from failing silently.

I believe this is better than silently dividing by 1.

It's not game-breaking fatal error anyway.

Former defaultValue is gone, because 1. It's set by onInit 2. It's better to restore the last value rather than something supposed to be default

TextFieldWidget -> OneLineTextField
StringTextFieldWidget -> TextFieldWidget

This reverts commit 8e00147.

This reverts commit 580683b.