Fix hovering state when target contains special characters

[panthony]

This PRs fixes the following issue:

• Donut/Pie issue with shown active arcs with some category #1794
• When the column name includes sign, C3 cannot tell the difference between signs #1687
• Problem in hiding parts of pie chart when clicked on legend. #1083 (probably)

CSS class names are NOT allowed spaces but every other characters is fine (https://www.w3.org/TR/CSS21/syndata.html#characters).

Since they are all prefixed by c3-targets- we do not have to care about the first character.

We simply need to escape in querySelector or in CSS if any.

I don't know if c3-target-XXX  is considered public or private api but this PR will break css/js based on this css class when target contains special characters.

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close #1687

[kt3k]

I confirmed this fixes the example of #1687

This change breaks the case when the data name contains special characters other than - and the user uses c3-target-XXX directly from their code. I think that's very rare usage. (possibly none)

The current replacing rule has an obvious defect, so I think nobody wants that behavior and it's ok to merge this.