Don't skip the preparation while starting a selection over an existing highlight.

This partially reverts 42909c058c9c3865f6254dfae03bdb2c883dc8e0.

Some explanation: since the selection activity is started, independently of the result if the (now disabled) check for an existing highlight (or other annotator-specific element),
it is not consitent for us to behave differently.

Here is an example. Create two annotations in a text, like this:

"whatever [long] text [here], and more."

If you start a selection inside the work "text", and move into the word "long", the viewer (with the annotation for "long") will not show up. That's intended.
However, if you start the same selection inside the "here" word, which already has an annotation, and then move into the "long" word, the viewer for long pops up, since isMouseDown was not set, because of this test.

I think this is not what we want, so I removed this test condition.

For protection agains annotating ourselves, we have other measures in checkForEndSelection.
(cherry picked from commit 6bee08c4bfa8606a05dd6ca55001df20b46a507f)
Re-Revert the behavior for the ViewerHideTimer (to please the test), but keep setting mouseIsDown even in these cases.
(cherry picked from commit 4e3c7c1c6c7a101f3cc6ae0ccaa94e904a392a86)
In cases where the container of a selected range lies within an existing annotation-hl, we want to find it's first parent that is _not_ an annotation highlight.
However, because of a bug in the jQuery selector, previously we were looking for the first parent that _is_ an annotator-hl - which was null in most cases, and an other annotator-hl in a few cases. (Which were then refused by the subsequent isAnnotator test.)

With this fix, now we can create annotations-within-annotations-within-annotations without any problems.
(cherry picked from commit 1eeb4abc144e1134a9de9bd789e01b38dede37d2)