Bevy build

[TimJentzsch]

This PR adds the remaining pieces needed for the bevy build command.

The command is a wrapper around cargo build, but with an additional web sub command which makes it a lot easier to build an app for the browser. I also plan to add additional features in the feature, like #68.

The PR contains the following changes:

• Added cargo install wrapper to install a program if it's missing (prompting the user).
• Added helper to obtain the current package name via Cargo.toml. There are likely better ways to do this (perhaps via cargo metadata), but I already had this implemented and we can improve it in a follow-up if needed.
• Added helper to determine the active compilation profile, which is needed to determine the path to the build artifact.
• Implemented the build command itself.

If you'd prefer smaller PRs let me know and I will split this up further.

[BD103]

In general, this change looks good! I love how easy dialoguer is to work with when prompting about installation.

I have a few comments and there are some merge conflicts, but then it's good to go!