Channel url and cursor fix

- Allow colons in channel urls
- Only add the channel part in the context menu
- Fix cursor not changing between separator and url

The last one only happens when the line starts with a url. When you first hover over the url or nick and then move the mouse to the separator, it will change to a resizing cursor. Moving it afterwards to either the nick or the url will not change it back to a hand cursor. Similarly, if you start from the separator, the cursor will be stuck as hand cursor.