Add proxy support and "Force HTTPS for GitHub" setting

[gmdfalk]

I use XCode with Alcatraz at work. My work environment requires a proxy for HTTP(s) connections.
Without a proxy, I cannot install plugins with Alcatraz.

This change fixes that by adding a new Alcatraz preference "Set HTTP Proxy". The value will be saved as a NSUserDefault and set as environment variable for both http_proxy and HTTPS_PROXY on shell subprocesses within Alcatraz (i.e. currently /usr/bin/git and (negligable) /usr/bin/xcodebuild).

The input for the preference can be any valid proxy host with an optional port, e.g. proxy.mydomain.com:9999.

This pull request also adds a second new Alcatraz preference "Force HTTPS for GitHub" to adress issue #214, although I have yet to see a plugin that uses the git protocol for the clone command. I've tried around 10 and they were all HTTPS.

Those preferences together with the packageRepo NSUserDefaults are now handled in a new utility class ATZConfig.

I'm sorry about the messy commits, I forgot to turn off auto-formatting.

Regards

[jurre]

Thanks @mikar, the PR is quite big so we'll need to find some time to review/test it, apologies for the slow response.

[jeeftor]

This would be great if it works!

[hefgi]

Any updates on this ?

[guillaumealgis]

I haven't looked at the code yet, but my first thoughts on the proxy thing are that if possible we should use the proxy settings defined at the OS level (in System Preferences). I don't remember having ever used an app where you could set custom proxy settings instead of relying on the system settings.
But then I don't use proxies that often, so I might be mistaken.

[gmdfalk]

@guillaume-algis
I have had to specify the proxy deliberately for many applications, despite setting the appropriate environment variables.
Examples: gpg (when fetching from a keyserver), maven (in settings.xml), IntelliJ, Eclipse, pretty much all Browsers, ...
It can be a drag.

Most command-line interfaces tend to work fine since they appropriately use the environment of the terminal, which can be adjusted on-the-fly.
But once a GUI application like XCode has inherited the environment from its parent process those it can't be changed as easily. The GUI has to explicitly expose the environment variables, usually via a Settings menu.

I think there are a lot of benefits to having an interface like this one (IntelliJ IDEA):

However, I haven't had access to an OS X system in almost a year and probably won't for another 3-6 months. I'd be happy to look into this issue again in a couple of months to solve this problem more appropriately via an Interface like above. This pull request was more of a quick fix, really.