Allow jumping between words on the input line

[DjMorgul]

Allow jumping between words on the input line when the focus is on it, with key combinations 'Command + Left' and 'Command + Right', instead of collapsing or expanding the channel list for the current server.

The later bindings were taking precedence even when the focus was on the input line (the BTextView to type IRC messages the user wants to send).

With the changes on this commit, when the focus is on the input line, these key combinations correctly move to the start of the current word or the previous word, or to the end of the current word or the next word. And when the focus is anywhere else, the behavior before this commit is replicated.

And the combinations 'Command + Shift + Left' and 'Command + Shift + Right' were also done to work correctly, moving the selection on the input line between words.

As the operation of expanding the channel list is harmless to the user (it will keep showing the server messages), and the collapse operation opens the server messages screen; changes the focus to the input line and moves its cursor to its end, 'Command + Right' will also expand the channel list if the cursor is at the end of the input line. This way the operation of collapsing the channel list can be intuitively undone by pressing 'Command + Right' right afterwards.

The opposite WAS NOT implemented, i.e. collapsing the channel list with 'Command + Left' when the cursor is at the start of the input line, because the collapsing operation hides the current channel messages (it's not harmless to the user's workflow).

[waddlesplash]

Rather than adding special logic here, maybe we should just remove these shortcuts entirely? Are they even used? CC @humdingerb.

If we are going to keep them when the text view isn't selected, then this code could definitely be cleaned up.

[humdingerb]

IMO both menu items to expand/collapse the "network list" (the actual outlinelist is weirdly labeled "Window list"...) do not need a shortcut. I've never used that shortcut, but always was annoyed the system wide ALT+left/right doesn't work when writing.

The menu items themselves aren't needed when we remove the shortcuts then at all IMO.

[humdingerb]

nephele on IRC pointed out that instead of those two menus there could be one: "Expand/collapse network" with one shortcut, e.g. ALT+E.
I think that's a good idea.