Add a context menu

[maxsrli]

Hi,

I understand this issue has been raised in one of the previous pull requests.

However, I think adding a context menu would be very useful, for example:

• UC1: Given a user has no, or difficult access to a keyboard (using a wireless mouse, remote projecting, etc), the user can enable PiP mode simply through the context menu.
• UC2: Given a user with conflicting keyboard shortcut, the user do not need to re-assign a new shortcut, and can enable PiP mode simply through the context menu.

Moreover, I have also added an option to disable the context menu for users that do not want this feature, the option can be found under Extension options.

Please consider adding this feature, thanks.