[Wishlist][WebUI] Show libtorrent version being used in Help->About

[Tim5000]

Please provide the following information

qBittorrent version and Operating System

qBittorrent 4.1.5 (nox)
CentOS 7

If on linux, libtorrent and Qt version

libtorrent 1.1.11
Qt version 5.9.2 in /usr/lib64
g++ (GCC) 4.9.2 20150212 (Red Hat 4.9.2-6)

What is the problem

Not easy to see which version of libtorrent is being used.
Would make it easier to fill in bug reports (maybe the full gui shows this?)

What is the expected behavior

On the WebUI show the libtorrent/libtorrent-rasterbar version compiled against.
Suggest on the Help->About page.

Steps to reproduce

Open "Help->About" dialog. Only shows the qBittorrent version

Extra info(if any)