improve the OS-X packages

[warner]

Our buildbot currently creates OS-X packages (.pkg installers) with each commit, but they're a bit disappointing. They install an icon to /Applications/tahoe.app, but clicking that icon only brings up a dialog box that tells you to run tahoe in a Terminal window. There is a /Applications/tahoe.app/bin/tahoe which can be run, but it's not in $PATH anywhere, so you have to type a lot or symlink it into a more useful directory.

(also, the packages are completely broken after the tox/pip/virtualenv switchover, but I'm hoping to fix that before the release).

The baseline fix would be to get bin/tahoe into a normal $PATH somehow. I don't know if applications packages can do that (CLI tools aren't a normal thing for .apps to offer). I've seen GitX and some XCode tools offer an Enable Terminal Usage.. menu item (which writes things into /usr/local/bin): maybe we could change the stub tahoe.app launcher to offer a similar option.

The longer-term fix would be to add a real launcher application. I don't think we have to go so far as to write a fully-native OS-X frontend for Tahoe. But I'd like something that behaves like the CouchDB launcher: a "Statusbar app", which adds a single icon to the top-of-the-screen menu (over by the wifi and clock icons). This icon leads to a drop-down menu with a few options: "Launch Daemon", "Open Web", and "Quit".

It would probably need a "Create Client" option which leads to a short dialog (maybe driven by a web page) that lets you paste in the introducer.furl and pick a client nickname, then creates your ~/.tahoe/ directory. Then start/stop/open map directly to tahoe start, tahoe stop, and tahoe webopen. Maybe throw in a rootcap/alias.

​RUMPS is a library that would probably make this easier.

Eventually it would be nice to have a proper setup application, so getting started with Tahoe felt nicer and more polished.