Cleaner hover icon for current selected node

[olibu]

This is a small fix to highlight to current selected node without hiding the object type.
Additionally to that the highlight is set in case of hovering at the hex view, too.

It now looks like this:

[lapo-luchini]

That red icon was a leftover of an experiment to have a hover-menu to click upon, was never intended to be there. I recently removed it with the "context menu" #82 changes.
I also added some bgcolor highlight in 6052316.
Do you think this is still needed?
If you have suggestions, can you base them on latest code from esm branch?
Thanks!

[olibu]

I don't think that this is required any more as of the current esm branch.
However, it's quite difficult to recognise the background color as the highlighting of the current selected path in the hoovered tree.
A "real" tree structure including buttons to open and close the sub tree would easier to understand in my opinion.

[olibu]

I have concept draft for a new interactive tree view based on the latest esm branch in my repository.
https://github.com/olibu/asn1js/tree/treeview

@lapo-luchini
What do you think about it.

[lapo-luchini]

I don't think that this is required any more

Okay! Then (if I didn't misunderstand your comment, else feel free to re-open it) I'll close this PR and we can talk about feature/treeview in #87. 👍🏼