[Enhancement] Add Default Environment variables to buildtools.json

[dansiegel]

Description

Adds the ability to add non-sensitive default values to the buildtools.json that are used by the Secrets class generator and the template manifest task. This allows both generically default variables and build configuration based variables.

The defaults can now be added in the buildtools.json as follows:

{
  "environment": {
    "defaults": {
      "AppId": "com.avantipoint.awesomeapp"
    },
    "configuration": {
      "Debug": {
        "AppId": "com.avantipoint.awesomeappdev"
      }
    }
  }
}

Given this sample I might tokenize the package name in the AndroidManifest or the CFBundleIdentifier in the Info.plist, this would then allow me to automatically set the name to com.avantipoint.awesomeappdev while debugging the app, and com.avantipoint.awesomeapp on all other builds. As a result I can easily ensure that I can deploy side by side instances of the app.

Issues

• Fixed issue with AndroidManifest only getting updated on subsequent builds. All manifest updates will now occur on a clean (first) build.
• fixes [Enhancement] Add Configuration based values #153
• closes Allow severity and default handling for missing Secrets #120 - this is really a better approach