[Python API] Add API to set session name and tab/window title
This is a bit of a glaring oversight. As mentioned in the iterm2-discuss thread "preference setting to prompt automatically for new tab names?", it would be nice to use get_string to prompt for text and then set the tab title. Since non-user variables are immutable by scripts (which is necessary for my sanity) I need to expose an API to set the tab title. Windows will need something similar, as will sessions.