add selection of element contents (e.g. text of current div) and its parent(s)

Created by: balcy

Currently if you long-press on a page, the current word gets selected, and the context menu offers "select all". So you can either copy/share the word or the whole page. (for inputs/textareas it is better because you can select the text in that with "select all") With this PR a new little feature "select element" is added, that allows to select the text / content of the element the context menu was opened in.

A typical use case for me is copying build / install instructions from a github / gitlab about page, and pasting them into the terminal app. examples I've used for testing: https://github.com/benni0815/SchafKopf http://docs.ubports.com/en/latest/userguide/dailyuse/libertine.html

Another case would be selecting one paragraph in a text only.