#366 Allow both Ctrl-Tab and Ctrl-PgDn for "next tab"

[Ram Rachum]

Ctrl-Tab and Ctrl-PgDn are both widely accepted shortcut keys for next tab. I want to be able to use both of them for Console2, but in the settings menu I can only set one shortcut key for "next tab". Please allow me to set two. (And preferably supply Ctrl-Tab and Ctrl-PgDn as default for "next tab".)

Ditto for Ctrl-Shift-Tab and Ctrl-PgUp for "previous tab".