Fragile first-run experience

**Describe the bug**

The initial project setup is a fragile process that can lead to user frustration.

If the user has a typo in the favicon URL, the Android project is created, but no key store. Trying to `build` the project leads to confusing password entry prompts and then errors. There is apparently no way to generate the key store outside of the `init` process. The user is left to repeat the entire project initialization.

**To Reproduce**

1. `bubblewrap init` a new project
2. Have a typo in the favicon URL
3. Go through the entire process of creating the project

**Expected behavior**

You get an Android project.

**Desktop (please complete the following information):**
- OS: WSL
- Browser [e.g. chrome, safari]
- Version [e.g. 22]

**Additional context**
Add any other context about the problem here.