feat: add command line argument to select/add tab with a channel

[Nerixyz]

Adds a -a <channel>/--activate <channel> command line option to activate a tab containing a channel or adding one (the feature request proposed --active).

• Only Twitch channels are supported (special channels are not supported)
• Only the main window is searched for tabs.
• If no tab/main window with the channel is found, a new one is added. When adding a new window, it will show an out-of-bounds warning, but it should be fairly rare that no main window is present (in that case you might as well specify a window-layout with -c).
• Tabs with fewer splits are preferred.
• Splits without filters are preferred.

Fixes #2498.