[ALOY-1235] Alloy: Improve how config.json conditions are handled

Currently, Alloy does a (shallow) merge of the different sections of the app's config.json and an optional theme config.json in the following [hard-coded](https://github.com/appcelerator/alloy/blob/master/Alloy/commands/compile/compilerUtils.js#L765-L846) order: * global * env:* * os:* * env:* os:* * os:* env:* I'd suggest the following change: Loop the config.json sections in the order in which they appear in the file and merge them when the conditions are met, just like we do with conditions in TSS and JS. Example:

{
  "global": {
    "foo": 1
  },
  "env:test os:ios": {
    "foo": 2
  }
}

Would be handles as if you'd do this in a JS file:

var cfg = 
if (true) {
  _.extend(cfg, { foo: 1 });
}
if (ENV_TEST && OS_IOS) {
  _.extend(cfg, { foo: 2 });
}

Use case: This is more transparent to the developer to see what the value will be if multiple sections are valid for the target environment and platform. It will also make it easier (less code) to introduce a new condition, as requested in ALOY-1210.