This PR does 2 things:

1. Pin the node modules to versions that actually work. The reason? I cloned the repo and built the package (worked) then installed the plugin in VSCode (worked), then launched on iOS (fail, without an error message anywhere). With help of npm view <package name> versions time --json I figured out what would have been the version of all (dev) dependencies in package.json at the time of the last release, and those worked just fine. So I decided to pin to those exact versions (and two of them with the ~ prefix as that doesn't do harm in those cases.
2. Save the selected iOS team id to a workspace setting. Closes Add option to save teamId once it is selected #138. The team id is saved in the workspace settings which can be removed by the user if he wants to switch to a different team. But I'm not sure anyone ever wants that within the same workspace, so no need for Add UI to select different Device/Emulator #137 which issue Add option to save teamId once it is selected #138 suggests.

Oh, as a bonus the Team ID picker's placeholder now reads "Select your development team" (it used to be empty).

Here's a short video showing off the changes to the iOS Team ID picker.

UPDATE: I've found the node modules that caused the crashes. The vscode-debug* 1.24.0 versions were fine, but there was an incompatibility with 1.25.0 and up (probably because their compile targets changed to es6). By upgrading this extension to es6 as well, the issue is fixed so we can upgrade to the latest versions of those packages.. but that will be done in a follow-up PR, along with a TypeScript bump to 2.6.x.